Here's some tips on spotting the scammers from the real premium models. Obviously, its not completely foolproof but it should help some.
'Live' snaps and Instagram live
So, you've added a model's public snap account from a code you saw from shoutout or on a takeover etc. A pretty good way of knowing that it's a scammer is if every post is uploaded from the memories feature and they never post anything 'live' and even if they do, they never show themselves on there. They often record stuff from legit model's premium or public accounts and repost it, changing the payment details in the process.
In the same vein, Instagram live can provide you with a way to see a model in real time, and get a legitimate response from them. However, this still isn't a way to tell if the model herself is trash and won't run with your money then block you.- but that leads me to the next point.
Being verified on legit (3rd party) sites like Manyvids, Fancentro etc.
This is a good way to check if a model who you think is legit, really is. The operators of those type of sites confirm a person is who they say they are, to be able to sell content on their platform- in a way that Twitter and Snapchat doesn't. Contacting the model on a verified site will allow you to ask them directly if any payment details you received was actually from them.
Them being on a pro site also shows that they will have a certain commitment to not do anything dodgy because it could impact on their reputation and therefore sales.
Recommendations from models you trust
Probably one of the better ways of getting a premium. If there's a model with whom you already have a great premium account with, getting a one they recommend will be a good choice. It could also be someone you've see them working with on snap shows too.
When I say recommendations, I'm not talking about models who's pages are littered with unverified snapcodes, from every 'model' who asks for one. Some models are more discerning than that and with them you'll often see the same few models being recommended.