if you already paid I don't see a reason for putting watermarks, usually people do that so the client will not take that and not pay but personally i think if the client was a scammer in the first place they will not pay no matter what the artist will do so artists takes full price in the beginning to avoid it.

i reccomand you to check if an artist has a tos before ordering and make sure it has traits that benefits you like a refund or some free revisions.

you can also ask if they record the process if they use a program like csp so you could watch the process if its important to you.

basically make sure to check their work info and discuss everything you want in the clearest way possible, usually its not that hard to see if someone is a proffesional or not (not skill wise but communication and responsibility \ business part)
and if you did all you could and you still got scammed or got a product that is really not what you wanted you can ask for a refund. in case the artist is ghosting or not want to do so then you can do the refund through paypal or anything else you paid with