Look for a track record. Who has he put where? Then ask those involved if it is true. Frankly, if he cannot get you a great label deal with support written in, who needs him???
Ask others who have dealt with the man.
Understand that not everyone gets along, so the more people you ask, the more accurate your info will be.
The cost could be anything. (Back Street Boys were paying out 75% in handling fees.) A manager would really have to be something special to get more than 20% from me.
Honestly, if I was out and gigging again, I'd be looking to establish a relationship with a good booking agent. I'd worry about management when someone started throwing record deals at me.
In any case, get EVERYTHING in writing, do not assume anything, and before you sign anything at all, make sure that you have an independent ENTERTAINMENT laywer (your uncle Joe who does property law is NOT QUALIFIED) approve it and explain exactly what the gibberish means, before you sign, before you sign, before you sign....
"I believe that entertainment can aspire to be art, and can become art, but if you set out to make art you're an idiot."
Show business: we're all here because we're not all there.