i don't know what works better but i did one time make a deal to get a discount on a session in the future and then it seemed she was always busy or not able to meet me. i did this twice and it was not a big deal. both times it involved laptops that i had upgraded out of and felt it was mutually beneficial till i never got the discount. now i just sell them and get my sessions the old fashion way. i pay for them!
anyway remember ladies if you offer the discount on a later session when the guy calls back try not to put him on the back burner. if he did you a favor you might want to put him first.