When the same item sells on both channels within the same minute, most sync apps are too slow to stop the second sale. You cancel the order, refund the buyer — and eBay records a defect against your account. Countlock exists to stop that one thing.
You have 2 units of one product left. Both channels are showing them.
2:14 PM
A buyer on eBay takes both of your last units.
eBay 0 leftShopify still showing 2
2:14 PM +6 sec
A shopper on your Shopify store buys the same 2 units.
Sold 4 unitsYou have 0
2:20 PM
Your sync app catches up and sets Shopify to zero. Six minutes too late — the order already exists.
Monday
You cancel one order, refund the buyer, and apologise.
Nothing here is anyone's fault. It's a six-second gap that opens every time two channels hold their own copy of the same number — and it opens widest during exactly the traffic you worked hardest to get.
The catch is that eBay doesn't treat it as bad luck. It treats it as your defect.
What one oversell actually costs
1A transaction defect on your recordeBay counts a seller-cancelled order as a defect, including when the reason is that you ran out of stock.
2Your Top Rated Seller statusTop Rated requires keeping your defect rate under 0.5%. If you're not selling in huge volume, a handful of cancellations is enough to cross it.
3The discount and the placement that came with itLosing that status costs you the fee discount and the search visibility — long after the refund is settled.
4A buyer who was ready to buy from youThey had your product in hand, as far as they knew. Now they have an apology.
What Countlock does differently
Four decisions, all aimed at the same six seconds.
1Checks constantly, not on a scheduleMost apps sync on a comfortable interval. Countlock checks both channels far more often, because the whole problem lives inside the gap between checks.
2Holds a unit back when stock runs lowOn your last few units, Countlock quietly keeps a small buffer in reserve on each channel — so the final one can't be promised to two people at once. You lose a sale you couldn't have filled anyway.
3Counts the sale when the order is placedNot when it's paid, not when it ships. The moment someone commits, the number moves everywhere.
4Tells you the moment a product driftsIf the two channels ever disagree, you hear it from us — not from a buyer. No silent failures, no discovering it in a review.
Before you get your hopes up
What we won't promise you
Every app in this category advertises instant, perfect, real-time two-way sync. We read hundreds of their worst reviews. That promise is where the anger comes from — so here is ours, with the limits attached.
—We can't make the gap zero. eBay's own instant-notification tools aren't dependable enough to build a guarantee on, for us or for anyone else selling you one.
—What we can do is make the gap small enough, and the buffer smart enough, that it stops reaching your customers.
—Countlock syncs Shopify and eBay. Not Amazon, not Etsy, not Walmart. One job.
—If that's not the problem you have, don't buy it. We'd rather lose the sale than the review.
Pricing
Priced on how many products you sync — nothing else. Every plan checks at the same speed and gets the same buffer, because selling you a slower version of the one thing that matters would make no sense.
Up to 500 products
$49/mo
or $490/year
A focused catalogue where a single cancellation still stings.
Most sellers
Up to 2,500 products
$99/mo
or $990/year
A real multichannel operation, where oversells are a weekly event.
Up to 10,000 products
$199/mo
or $1,990/year
High volume, where defect rate is something you actively watch.
More than 10,000 products? Email and we'll quote you honestly. Annual billing is ten months for twelve — the discount is real, not a countdown timer.
There are eBay sync apps for $9.99, and you may well have tried one — most people reading this page have. Cheap sync is cheap because nobody is being paid to sit and worry about the six seconds. Here, that's the entire product.
Billed through Shopify. It appears on your normal Shopify invoice with everything else — no separate card, no separate receipt, and VAT handled for you. Cancel from your admin in two clicks, without emailing anyone for permission.
Questions
Does this work with variants and multi-SKU listings?
Yes — variant and SKU matching is where most sync tools quietly break at scale, and it's a core part of what's being built. If a SKU can't be matched confidently, Countlock will tell you rather than guess.
I sell on Amazon too. Will you add it?
Not for now, and possibly not ever. Doing Shopify and eBay properly is a full job. If you need four channels synced, a broader multichannel tool will serve you better than we would.
What does "holding a unit back" mean in practice?
When a product drops to its last few units, Countlock stops listing the very last one as available on both channels simultaneously. You may occasionally sell one fewer item than you technically had. In exchange, you don't cancel orders. You can turn the buffer off if you'd rather take the risk.
How do you count products for the plan limits?
By the number of products you actually sync between the two channels — not your whole Shopify catalogue. If you list 8,000 products on Shopify but only 400 of them go to eBay, you're on the $49 plan. Variants of the same product count once.
Will there be a free trial?
Yes. You'll be able to run it against your real catalogue before paying anything, so you can see the drift it catches on your own products rather than in a demo.
Who is building this?
One engineer, working on this alone. That means no sales calls and no phone support — but it also means the person who answers your email is the person who writes the code. Replies come within a day, in writing.
Get told when it's ready
One email when Countlock launches. No newsletter, no drip sequence, no sales call — and everyone on this list keeps their launch price for as long as they stay subscribed, whatever the public price becomes later.
The optional question decides what gets built first — nothing else. Your address is stored to email you once, and never sold or shared.
You're on the list. You'll hear from a person, not a robot — and only when there's something real to show you.