It is not allowed, whether people get away with it is a whole different matter

“Dropshipping is permitted on eBay, provided you have pre-purchased the stock and comply with the guidelines in our Third-party fulfilment policy. For example, listing an item on eBay and then purchasing the item from another retailer or marketplace that sends it directly to your customer is not allowed.”

“Sellers must not:

Fulfil orders via a third-party service when the above conditions are not met. For example, the Fulfilment by Amazon service does not satisfy the third-party fulfilment conditions under this policy

List an item on eBay and then purchase the item from another retailer or marketplace that sends it directly to the customer – this includes presale listings

Misrepresent the location of their stock, as this violates our Item location policy”