PSA if anyone was confused by this or whatever:

1) You can not trade in dungeons/instances, so it is impossible to tip inside anyway with random people.
2) It is against ToS to offer services for gil in the Party Finder (aka "Mercenary Work")
3) It is NOT against ToS to "hire" someone to join your party. Obviously you'd be offering to pay and should tip in this situation.
4) This is most likely a joke thread anyway; I've never even heard of this as a thing.