Converting Mp3 to Flac is either stupidity or deception...

Freeware "Trader's Little Helper" can be helpful in testing the integrity of downloaded Flacs.

Expand the flac back to wav, and then run Trader's Little Helper test
to determine if there is a high probability that the file is genuinely lossless...

I'm sure there must be other test methods by now.

I'm years behind the times in these matters...