please advise any issue with a dropshipping business, which means you list items for sale that you don’t have in your hand but you can get from partner or friend later. should I inform in advance or there is no issue with this? any source? thanks

The answer is yes, that today, being that this is a known and accepted practice and framework, the Chatam Sofer and most authorities allow it, based upon the concept of Situmta, where the types of halachic acquisition are broadened, based upon what is accepted. I imagine it will be difficult to find sources in English for such technical concepts.