I don't know whether award ticket receipt still show the (sub)fare class for award tickets, but if you see a two letter code such as ON rather than a single letter such as O for business class, it isn't low. At some point, someone here posted the hierarchy of the two letter fare class class codes for award tickets. DL permits free cancellation by midnight of the day after an award (or other) ticket is purchased (IIRC with the exception of award tickets within 72 hours of departure) so if you get a receipt that shows two letter codes, you can then decide whether to cancel.