So Fiverr for those that aren't familiar is a site for buying and selling creative works essentially, from freelance artists. On some of them you can "add on" either (a) "Commercial Use Rights", or (b) "Full Broadcasting Rights". Most authors don't seem to mind about these things and instead make copyright free works and when asked will say "Of course you can use this however you like" sorts of things.
Meanwhile, there are the lawyers saying everything needs to be in a contract. Fiverr doesn't have any "contracts" other than your purchased transaction if that counts. You're left to wonder if you need to go out beyond and write up a "Content License Agreement" sort of thing that officially outlines everything in legalese.
My question is, broadly, what are the rules/laws for sites like Fiverr in terms of using the content you purchase? Doesn't purchasing it mean you have full rights to it?
If not, then what actions must be taken to ensure you have "full rights" to the content? Purchasing these "addons" hardly seems like a robust solution, would that even hold up? Does asking them casually in chat "Hey, can I use your content for commercial purposes?" and them answering "Yes of course :)" count as a contract? I think it does, but maybe I'm wrong. And if they instead say "No, you cannot use it for commercial purposes", what do you do then? Or perhaps they say "No, but if you buy my extra gig you can get the commercial license", how do you make this binding?