Sure...why not?

I've mastered some 15 second commercial spots and jingles.

It doesn't cost any less than a single track of mastering, but then again, I'm pretty cheap.

Master the track and send the bill. If he freaks, then you know he was misled as to what mastering is.

On what medium did you receive the loop?

If you were sent a CD-R, is it possible that he just didn't check the tracks before he sent them to you, and that this is a case of a CD burner screwing up?

He emailed it to me, .wav file.
Mastering jingles and commercials seem kinda different than a 5second loop to me...

Yeah, kinda weird.

I'm with Jeremy, do it and bill him.

If he raises too much of a stink, ask him what he thought you were going to do to it.

why not just ask him?

Oops, I thought I added that earlier.

Yeah, why not ask him?

Kind of senseless to "master" (and I use the quotation marks for style in this case) something that isn't finished.

I certainly wouldn't want a loop tampered with dynamically... It may well not actually be a "loop" when it's done.

Jingles and commercials, sure. They're done. Even music beds (assuming there isn't going to be any excessive compression or limiting done to it). But "mastering" a loop would be like "mastering" a vocal track...

It sounds like this guy has sent you the wrong file or something has happened to the file in the process.

As mentioned before, ask the guy if this is actually what he wants done.

I can't for the life of me see why he would want a 5 sec loop mastered for djing purposes, maybe ask him what he plans to do with it?

ya he sent me the right file, he basically wanted me to clean it up and do something about time stretching...but it sounded grand, timing wise.

Massive Mastering wrote: But "mastering" a loop would be like "mastering" a vocal track...

Yes and this happens. Some clients are expecting a big choir with complex harmonies after Mastering... with a solo vocal distorted track.