eBay | Amazon
How to turn off image sync and manage images directly on listings:
eBay
Go to Listings > Bulk edit. Then click Columns
Select Catalog Image Sync then click Done.
Scroll right and look for 'Catalog Image Sync' column, then toggle On/Off as required.
OFF eBay listing will NOT be updated from your Shopify images i.e. you can change it on eBay directly and it won't be overwritten.
ON Images are being synced from your Shopify to your eBay listings (changes directly on eBay will be overwritten).
Amazon
For Amazon select “Send Offer Only” in the Send Listing Details. This allows you to manually adjust in Amazon Seller Central.
Note, turning off syncing listing details also stops syncing titles, descriptions, etc. (For a full list of fields click 'show' and scroll right).
Currently, there is no ability to only turn off image sync.
Send Offer Only
Only Price, Inventory, and Shipping settings from Marketplace Connect settings are synced with Amazon. Other elements of the listing use the existing Amazon catalog details such as Images, Titles, Descriptions, Bullets, etc.
Send Product Details
All listing elements from Marketplace Connect are synced with Amazon.
Note, Shopify Marketplace Connect will sync with Amazon Seller Central - that does not guarantee that the Amazon catalog entry will update, Amazon will then use this data at their sole discretion.
For further assistance, please reach out to marketplace-connect@shopify.com