When I was producing events, I did a lot of stuff that had sponsors and underwriters who contributed in some way( facilities and services as well as cash) so I tended to offer fees, rather than either guarantees or percentages. This made things easier, and often (but not always) made performers more comfortable.

We started offering fees for smaller, unsponsored events too. Some of our people had the the "What if it rains" jitters, but the opposite turned out to be the case, and we built up a decent cash reserve, and that allowed us to do a few things that were interesting, rather than just worrying about who would sell seats.