A semi-regular client has expressed interest in having a threesome with me and another woman. I'm used to working alone and don't have many friends in the industry (I'm quite new and have few networks). Can anyone please offer any tips on how to go about this? He is well behaved and reliable enough that I'm seriously considering doing this, but for more money than 1-on-1 sessions.

I'm thinking that the common sense things come first, like finding out how much we should charge and getting a deposit (he usually pays me upfront cash) and getting a full panel STI test result to show to a prospective duo-partner. Is there anything else really important? Chemistry? And where is the best place to find someone? Is it appropriate to respond to other service providers' ads or will they think I'm a scammer?