It is quite telling that you employ the use of drugs as an alternative example to religion. Eitherway, I CAN sue you for selling drugs you cannot prove work, IF you have made the claim that they do. For example, if you advertise that your drugs help with sleeping disorders, but they actually make your hyperactive (or don’t work at all) then I can sue you for fraud because that’s what it is.
Definition of fraud: “An intentional perversion of truth; deceitful practice or device resorted to with intent to deprive another of property or other right.”
By saying that your product does something that I can prove it does not, such as the example with drugs, means I can definitely sue you for fraud since you’re trying to gain some of my property in the form of money. However, making unverifiable claims to gain money isn’t much better, and I’m sure that many religious teachings can been classified as inducing various psychological conditions. See this study: http://deseretnews.com/dn/view/0,1249,660199036,00.html
I don’t need to wait till the (imo non-existant) afterlife to sue you. That’s just silly. There is so far not one shred of evidence to show that the afterlife exists. Which means you’ve created a win-win situation. If the afterlife does exist, then you win and your god saved me from hell. If it doesn’t, then you lose nothing since I can’t sue you in this life. Pointing this out to a court, together with linking to many studies about the effects of religion on people’s minds, explaining how you may very well be lying to get my money, etc. would definitely form a very serious case against you.
And to answer your other question, of course I must be part of the transaction. However I don’t see why you dismiss the possibility that someone who converted from whatever religious group it is you advocate, to another one, may very well sue you on the basis that you deceived them, making the arguments I pointed to above.
You for some reason assume that you not only deliver a “service”, which I find in itself dubious, but that people would be satisfied with it. To put this into perspective, answer me this: If god is on your side, why do you need money from people who go to your church? I’m sure your omnipotent god can help you out some way, maybe not directly, but indirectly influencing your luck with money or whatever. All stuff to think about.