If you pay for a whore, you don't expect to be fucked in the ass yourself (at least, I don't...)
You tell them exactly what it is, no exception made. If it is an exotic tryptamine analogue that causes LSD-like effects, you tell them it's not LSD but LSD-like, and that they just need a higher dose. Jonathan Ott's masterpiece Pharmacotheon contains a very interesting passage about ppl who claim to have used mescaline, while they probably have been tripping on LSD.