I’ve noticed some sites only accept MP3s (such as MusicDealers). Can such sites be taken seriously, as surely any music supervisor/sound editor would want a more Pro format such as AIFF or WAV. Or am I just being old fashioned?
Yes, take them seriously. Most music supervisors listen to them in MP3. I know of one music supervisor at one of the premier trailer houses that listens only to MP3’s on iTunes.