Personally I expect it to get out of hand once the platform gets more real users, but since its so decentralized the solutions for that will also be decentral.
So what the exact solutions will look like is to be seen, but I assume a mix of verified relays, Web of trust (Nostrudel has this where you only see content from people you follow, who they follow, and who the people they follow follow) and just general anti spam detection. I wrote a basic anti spam detection for a prototype I made to, and it actually caught a surprising amount just by monitoring how quickly accounts post and how similar their messages are.