I noticed that you cannot invite people to treasure rooms. Yet people can be invited to the floors where random recipe vendors are at? I am not sure if this was intended but people can make money by sitting at Tier 3 floors and selling invites for the recipes there.
I know most will probably be upset if I suggest this but maybe we shouldn't allow players to be invited there. It doesn't seem right to allow others to make money just sitting at these floors.
However, if this was intended and deemed a very acceptable way for stronger characters to make money, then by all means don't change it. I'll give it a try one day when I get that far.
You don't even need to be a strong player, just buy a teleport from whoever is selling, then click party options, Go Solo, and you now have the ability to invite to the same level they were inviting to.
I am somewhat with you in it seems like a very skeevy way to make crowns, you take none of the risk of buying the recipe and gain all of the benefit of the finders fee. That said, I have used recipe teleport services twice, they are very convinent and a cheap way to buy T3 recipes.