They're making ample use of a recreational drug, but it's a distilled liquid. Have they ever trashed a song? I'm just asking.
I've never fully figured out their rating system. Mostly, they seem to have a very top tier. Then A+ A A- etc. Don't recall anything lower than a B+ but I most certainly have NOT watched all their stuff - yet.
I think they start from source lists CREATED by their fans. So, when they get 1000 (SWAG) requests to review a given song or artist, they'll try to work that in. So, there is a certain level of pre-selection involved I think. IOW their fan base has an idea of what THEY like and I think their fan base hope they like what their fans like - so put their BEST picks out there for review. Like I said - "pre-selection" to a certain extent.
So, let's say I were to suggest to them a song by Rod Stewart (I haven't, and I wouldn't - I don't interact in such ways on the big, scary internet - this is close as I get here on the FIRE forum!) BUT if I DID, I would not suggest they review Rod's "sweeter, softer side" like YOU WEAR IT WELL. I'd go for the "down and dirty" like FACES doing STAY WITH ME or the Classic MAGGIE MAY (IIRC, they HAVE reviewed at least the FACES song.)
It's funny that their fans (or they?) seem to think as I think about folks like Bob Seger. I can't recall exactly, but IIRC, maybe in the context of NIGHT MOVES the Duo brought up that Bob had done some really early song - they thought some fans had suggested RAMBLIN' GAMBLIN' man. In any case I was thinking YEAH! THAT is CLASSIC Seger. THAT kind of song is what attracted me to Seger back in the day.
SO, their fan base already sets the bar quite high for these guys to chose from IMHO. It appears that by now, the duo "trust" their fans and the fans trust the duo. I don't think the duo would fail to "trash" a crappy song - even if it had a strong fan base. I just think it highly unlikely their fan base would ever recommend a crappy song. Heh, heh, I could be wrong. I was once.
So that's sort of my long-winded way to answer your question. I need to get back into watching as I've let some other stuff crowd that part of my life out of late (travel and medical issues can interfere with "important stuff" like music!) YMMV