Don't know if it's a scam, but the user has pretty good feedback, so I doubt it.

What's strange is this Q&A answer from the listing:

Q: Hi-What type of certificate is this? Can you use more than 1 world perks acct #-example to get enough in each acct for Hawaii? Thanks for your time and hope we can do business.
A: I received 4 certificates for an international flight which was 8 hrs late. These have no names etc attatched to them and anyone can use...

Seems to be excessive compensation for a delayed international flight. Even if there were 4 travelers and each got a cert, 25K miles seems hefty.