Wow! What is it with clients wanting to manipulate the meaning of a GC purchase around here lately?
I don't have any ideas for what to tell this particular client, but I do have a suggestion for the GC wording. "The Superior - a 90 minute massage ($70 maximum value - not redeemable for cash - must present original certificate to receive goods/services - office appointments only)
Maybe that way it is clear that it is for one specific service, AND that there will be no more than $X worth of goods & services delivered, AND it might even cover that situation where they come in for a massage 2 years later and your prices have gone up. Oh, and the outcall situation too. (I don't think that was you, but it came up for somebody else recently.)
I am going to have to redo my GCs. I haven't had any problems, but I am always interested in keeping my glutes draped, so to speak.