Anyone doing business over Instagram is a fool IMO. There are too many scams there.
Nonetheless, if you pay via PayPal you will probably be safe enough, as PayPal does tend to favour buyers fairly well. If on the other hand they ask for crypto, bank transfer, Western Union etc., run a mile unless you are really sure about them.
Chances are they don't really have the part, they'll go out to someone else who will, add a markup and ship onto you - that's if they don't run off with your money. They may do the typical Win-Source thing and come back to you asking for more money, or offering an alternative-but-compatible device (in so far as it *looks* the same, even if it's completely different chip).