Apply this test and see how they score.
Phone Number: Is there a phone number prominently displayed on their home page. Red Flag if there is not.
Address: Do they have a physical address posted? If not Red Flag. If they do have an address, what does it look like on Google street view or satellite map? Red Flag if it doesn't look like a business.
Inventory: Do they have a lot of hard to find stuff or too good to be true pricing? Red Flag if they do.
Business History: When you Google the business name with the words review and complaint, what do you find? Little footprint or a lot of negative reviews or BBB complaints is a red flag.
Payment Method: Crypto, Venmo, Pay Pal friends and family only? Red Flag.
Site Language: Do you notice language errors or irregularities? Red Flag if there are errors and oddities.