Sellbrite

Great little app, I have been using it for years with few issues. It's the only app around with a useful free plan that can sync your Shopify store inventory with Etsy and Ebay. Very easy to use.

Products are syncing when we publish on sales channel for the first time.
After that there is no real time syncing of price and inventory. So we had oversold products.
Support is very fast but we only get basic and generic feedback.
Videos are very basic.
Nobody really looks at our issue.
Cannot resolve issues.

I have now received the information that free plans sync only every 2 hours and paid plans sync every 15 minutes. This clarifies my issue, but I had not seen anywhere this information before. With free plan you still have the risk of overselling if you get an order within the 2 hour sync cycle. I changed my rating to 3 stars.

New update: this app is definitely not syncing correctly. We had 2 orders on eBay for products no longer available. We had to cancel the orders. Not good for customers, not good for complying with eBay policies. It looks like the "eBay listings" on the app do sync with listings on my "base" inventory downloaded on the app. But the eBay listings on the app do not actually sync with products already listed on eBay, after having listed them on eBay from the app. The sync only happens the first time they are listed on eBay, but no sync afterwords with eBay. These orders were in fact no longer in stock since August 25!! Still showing available on eBay. No longer showing available from the products downloaded to the app.
Avoid this app to avoid embarassment with customers and risk for not complying for eBay rules. This can be very costly.
We have about 20,000 products, of which 622 on eBay. Impossible to keep checking each and every product one by one.

We’ve been experiencing serious issues with Sellbrite allowing Amazon to oversell our inventory for over a month now. Initially, we assumed it was a mistake on our end, but after closely monitoring the situation, we discovered that Sellbrite was not syncing any inventory data from our Shopify store.

Multiple products that are marked as drafts with zero inventory in Shopify are still showing quantities of 5–10 in Sellbrite.

We reached out through live chat in hopes of resolving the issue, but after waiting seven days with no action taken to even open a support ticket, we’ve had enough. We're removing the app from our store and actively seeking a more reliable solution.

If you're a business managing a large catalog and need accurate inventory syncing with Amazon, this is definitely not the solution.