Q: Is it legal to connect to eBay's API if I use a real wholesale supplier (not retail store)?
A:
eBay's problem is really with retail arbitrage dropshipping, not wholesale. Please refer to their User Agreement --> CLICK HERE
Also, eBay's rules on price gouging -->> CLICK HERE
Lastly, here's information related to using the API for retail arbitrage (since essentially a retail supplier is also a competitor of eBay's). See screenshot:
Here's the link -->> CLICK HERE see section 9.7.
Sku Grid and its repricing methods (whether API or not) can be used to revise wholesale items, which do not fit that disqualification criteria.