I'd be interested to know what people's experience is of bitrate checker programs and which ones seem to do the best job...
Myself, I have Fakin the Funk, which in general seems pretty accurate although can sometimes bring up false positives.
I just heard mention of Lossless Audio Checker here on the forum so gave that a try.
It doesn't have the same false positives as FTF, but one obvious problem it has is when checking classical music or "quiet" albums such as acoustic & vocal.. all my classical music came out as "upsampled" even though I know for a fact it isn't.
Ultimately, I prefer to trust my ears and can easily pick out a 320 mp3 next to a flac or wav file, although could be (and have been) fooled if all I'm hearing are 320 mp3's