I can look at the incoming transaction and figure out its inputs, can't I? I then know who the sending address is. If I had a mapping (internally) from the sender address to some business service or product I need to sell to them, then I can validate at this point that the payment was made from them.
There could be multiple inputs, I realize, and that is a challenge in itself, but each incoming TX has this info.
On my original question then -- there is no effective way then to advertise a service and tell people to pay to that service.
And what about something like SatoshiDice? They have published vanity addresses. Lots of companies are doing vanity addresses to receive payments. Are these all at odds then with "best practices"?
Just wondering what the best way to go here is. I am trying to establish a service where the pay-to address is not constantly changing.
If so, then how do I do this? What if I wanted to (just a silly example) print t-shirts or put an ad out on the newspaper or a tv commercial saying pay to this address for some purpose -- you are saying this should not be done?
Perhaps just think about this from your own side - how do you know who has paid if all payments are made to the same address?