How are you authenticating the designer items you buy from thrift or goodwill stores before selling them? As a seller it is your responsibility to ensure the item you are selling is authentic.

Personally, I have seen many fakes and knock offs at thrift, consignment and other resale stores. There are a handful of brands I am confident enough to authenticate on my own and there are many forums where folks have years of experience and will offer their input if something is authentic.

Many people may donate fake or inauthentic items because they can not sell it online as it is not allowed.

Goodwill receipts will not prove the item is authentic. It proves that you bought it at a Goodwill. Asking for receipts is their attempt to prove brand purchase and authenticity.

IMO - Make sure what you are selling is authentic or you may end up banned on all the platforms or worse.

Just some friendly tax advise, depending on how much you are making you need to keep receipts/totals for tax purposes.