Read this before you crosslist anything

Warning: how our crosslisting tool actually works

I would rather you have all of the information first and decide against using this than buy it without knowing what it does. So this page is the whole thing: the mechanism, what we can and cannot see, what breaks, and the one risk that matters most.

The short version, before any of the detail: crosslisting to Poshmark, Mercari, Depop or Vinted breaks those marketplaces’ terms of service. Not just ours. Every crosslisting tool that exists. If that sentence is a dealbreaker for you, stop here, and I would rather you stopped here than found out later.

How it actually works

There is no official door. Poshmark, Mercari, Depop and Vinted do not publish a seller API that lets a program create listings. eBay does, which is why eBay is the one place FlowLister posts directly from our servers. Everywhere else, something has to fill the marketplace’s own form.

That something is a Chrome extension called FlowLister Crosslister, and it runs on your computer, not ours. The sequence is:

1. Our server takes a listing you already made and builds the content for the destination marketplace — title, description, photos, size, price, category.
2. That becomes a job in a queue on our server. Nothing has touched the marketplace yet.
3. The extension, running in your Chrome, claims the job and fills the marketplace’s form inside the session you are already logged into, as you, from your computer and your IP address.
4. It reports the outcome back so the listing can be tracked and ended later if the item sells somewhere else.

So the honest framing is this: the tool does the clicking you would have done. It is faster than you and it does not get bored. That is the whole advantage, and it is also the whole problem, because a marketplace watching for automation is watching for exactly that.

What we never have

We do not have your Poshmark, Mercari, Depop or Vinted password. Not encrypted, not hashed, not held briefly. It is not in the system. The extension uses the browser session you already opened, which means we never need the credential and could not sign in as you if we decided to.

The extension also does not use your FlowLister login. It carries a separate, narrower token that can only drive crosslisting for your account, and that can be revoked on its own without touching your FlowLister session. If the extension were ever compromised, that is the blast radius.

What it posts to, and what it does not

Being precise here matters, because “supports five marketplaces” can mean five very different things.

• Poshmark and Mercari can run unattended, where a rule posts for you without you picking each item — and only when the item clears conservative checks on category, weight and a real shipping quote. We do not guess a parcel.
• Depop and Vinted are manual. You choose what goes, item by item.
• Etsy creates drafts only, and Etsy’s eligibility rules for handmade, supplies and vintage are yours to satisfy.

This is a young feature. Poshmark is the most reliable path by a wide margin because it has had the most work. Mercari and Depop fail more often than Poshmark does. Vinted posting has never completed successfully for anyone, and I would rather write that sentence than let you find it out yourself.

The risk, stated plainly

Automated posting is against the rules on every marketplace this tool touches except eBay. I knew that when I built it and I authorised it anyway. Here is what that can actually cost you.

• Your account. A marketplace that decides your activity is automated can remove listings, limit your features, suspend you, or close the account for good. No FlowLister seller has had that happen so far, and I am not going to dress that up as a safety record — few people are using it yet, and past safety is not a promise about next month.
• Selling the same item twice. One item listed in three places can be bought in three places. The sale detection exists to close that window and it does not close it instantly.
• Breakage without warning. We are filling someone else’s form. When they change it, posting stops working until we catch up.
• Your computer is the engine. No Chrome open, no posting, and no sale checking on the marketplaces without an API. A laptop shut for a week is a week those listings went unchecked.
• Buyer experience. If a crosslisted item sells elsewhere and you cancel, the cancellation lands on your record on that marketplace, not on ours.

What we do to reduce the risk

None of this makes crosslisting compliant. It is not a loophole and I am not going to present it as one. What it does is keep your account from behaving like a robot, and keep our mistakes from becoming your mistakes.

• A hard ceiling of 10 new listings per marketplace account, per rolling 24 hours. Not a setting you can raise. It is enforced on our server when a job is handed out, so a retry, a second browser window or a second machine all hit the same wall. A burst of posting is what gets accounts flagged, and this is the single most important thing in this list.
• A circuit breaker. When we see repeated signs of trouble — a bot wall, a logged-out session, a transport failure — posting pauses instead of retrying into it. Hammering a marketplace that is already unhappy with you is how a bad afternoon becomes a closed account.
• It cannot post the same item twice. A job is claimed by one worker atomically, the exact fields are pinned at first claim so a retry submits what the first attempt submitted, and we record that a job crossed the submit boundary before it crosses it. A timeout or a retry makes us go and check whether the listing already exists rather than create a second one. We learned this the hard way on eBay, where a create-timeout once double-listed real items.
• Conservative gates on unattended posting. An item only goes automatically when the category is supported, the measurements are real and a native shipping quote actually comes back. If we would have to guess at a parcel, we do not send it.
• Sale detection that does not depend on your laptop, where it can. eBay and Etsy sales are read on our servers through their APIs, so they are noticed whether or not your browser is open. The delist is then queued on our servers too — a closed laptop delays the delist rather than losing it.
• Sale signals read from your own account, not from a badge. On Poshmark we read the inventory counters on your listing and record a sale only when every unit is gone. A “SOLD” banner on a page can belong to somebody else’s listing, and acting on one would end your eBay listing for no reason.
• A separate, revocable token. The extension never holds your FlowLister login, and it never holds a marketplace password, because there is not one to hold.

Why I built it anyway

I am a reseller. I do estate sales, I like vintage, and for years the listing was the part that buried me. Putting the same item on a second marketplace doubles the chance it sells and roughly doubles the typing, which is why most people say they will crosslist and then never do.

I looked at the rules, and I looked at the fact that these marketplaces have chosen not to give sellers a supported way to do something completely ordinary — put your own item up for sale in more than one place. I decided the trade was worth it for my own business before I ever offered it to anyone else’s.

So: I think it is worth the risk. That is a judgement, not a fact, and it is mine rather than yours. You have the whole picture now — read it, decide for yourself, and if the answer is no, keep using FlowLister for eBay and leave the crosslisting switched off. That is a completely reasonable place to land and it costs you nothing with me.

Chris TaylorFounder, FlowLister. The support email comes to me.

Questions people ask before turning it on