Global Blue's been doing this on VAT refunds for some time:

http://www.globalblue.com/customer-s...shopping-faqs/
http://www.globalblue.com/globalblue...thodsTerms.htm

Seems they've done this with impunity for refunds.

If Airbnb gets away with doing this for charges, I won't be surprised if other disreputable merchants take this up.