Wells are the biggest draw because there is at least a custom going back into antiquity of using sympathetic magic and the power of healing afforded by sacred wells and the nearby sacred trees. The original sentiment was certainly not one of you got nowt for nowt, but rather that you got nowt without following the proper method. In a time where giving a gift that could be termed a "possession" to the otherworldly beings that were thought to be mankind's helpers, you DID get nowt for nowt in some cases. (Yes, thats what the Potter elf who is given the sock was based on, most of it has origins in folore of one country or another). It's an ancient custom bastardised by modern "pay for salvation" and "capitlist bargaining" type thinking. Not to mention the bastardisation of the beliefs behind such customs by mixing them with other cultures and time periods.

The whole "the spirits will tell you if you are doing it right or not" would seem to be a get out clause being trumped out as an excuse.