This is probably true for all such sites, but I would be particularly careful with a vendor like Vayama. Recently I purchased a short hop trip on JAL through Vayama, and the fare rules which they gave me were labeled YKJL. When I looked online a bit later, though, I saw that I had been booked into H class. I still haven't gotten a straight answer about what went wrong (if anything at all.) But buyer (who is interested in frequent flyer miles/points) beware.