Here it sounds like the guarantee means there will be a flat amount that you will get - then any further profits up to 10% will be yours? This is my understanding, but honestly, you won’t look silly just asking for clarification on that. Very normal. Don’t be afraid to ask - you won’t come across as a newbie, you’re just watching your back. They will be used to this, believe me. I’d definitely try agreeing to a flat minimum so you don’t walk away with nothing if it goes balls up - at the end of the day, you still did work that should be paid for, regardless of result. As Theo said though, might be worth seeing what happens and learning from the experience, as tends to be the way. I guess it’s up to you though to figure out whether you’re willing to risk that. I don’t think there’s anything malicious going on here, and 99% of the time you should be fine - but you have to accommodate for that 1%.
You’re better to be shrewd from the onset, rather than get yourself in a position where you’re having to claw your way back up. Don’t underplay your worth, especially in the entertainment industry. It’s better to ask / expect more from the start than have to justify more in the future. From experience, people will come to expect you being quite lenient, and be more annoyed down the track when you try adjusting your expected cost. It shouldn’t be that way, but unfortunately it often is.
I do feel in situations like this though it comes down to the kind of client you’re dealing with, and it’s up to you to read them. If you’re just wanting to get your name out there though, then maybe go for it.