I see. I'm guessing you're basing this on his Dembélé Tweet yesterday, right?Going off a reliability scale from Reshad Rahman Foot Mercato are supposed to be reliable.
Anyways, Reshad Rahman has stated in the past that he rates reports, not sources, for their reliability. On Foot Mercato specifically, here's what he said about them in 2020:
I'd consider this a generous comment on them, too. They're the French version of CaughtOffside: they are very speculative but have 1-2 journalists who get hits from time to time (Santi Aouna, Sébastien Denis).