It's quiet - too quiet.

Mr snuggles deserved a dex saving throw :(

Shitlicker the Quasit did not.

Are there marks left behind on the floor from the fire and dead animal? Yeah? So, you're telling me this 30x30 foot stone room with a flame trap has never been set off before? My familiar is the first creature to die in there? Whoever built it never tested it? Because burn marks on surfaces would have been something special about the room... Now, give me back my familiar and DM better.

A gelatinous cube rotates through the area every 8 hours to hoover up any leftover char
- And it doesn't set off the trap when it comes through, because why?
Fire itselt doesn't necessarily leave marks on the stone floor unless it's long and hot enough to melt stone, that's just byproducts of stuff not burning properly.
The testing familiar -just like yours- didn't leave any traces in all the trial runs, it just vanished to its realm of origin.
Now, continue playing your class instead of cosplaying as a rules lawyer.
- It's uhhh a propane flame so there isn't even any smoke
  Also, the whole dungeon has been covered in a layer of grime since you walked in. You aren't gonna notice a bit of residual soot.
- Take a lighter to a rock. Fires leave char. There are very few combustion systems with a pure enough burn to avoid it.
  That's not rules lawyering at all. If a player asks why they didn't spot that the easy answer is they didn't realize it was char.
The room is pitch black, you're relying on dark vision, and you just failed your perception check. I can definitely see this happening outside of bad DM'ing, and I think the PC being sus of a blank room in an otherwise dangerous dungeon could also be in character.
Dawg the point is to have fun with your friends, not win vs the DM in a game of semantics about why they haven’t spent 10 hours of their week crafting a world for you for free
Familiars don't leave corpses.
You think they wouldnt clean the trap after every activation? Leaving scorch marks wouldnt make for a very good trap would it?
- Ever tried to clean a pizza stone? Pretty sure that magical fire is supposed to be hotter than the 400 something degrees my oven gets to in using one.
the janitor has a deactivation key
Punishing reckless players doesnt hurt sometimes
- Ignoring hints is recklessness. The only hint that there is anything off about the room is that the DM says that there isnt anything special about it.
- How would carefully examining your surroundings be anything but the opposite of reckless, though. Annoying, perhaps, but that's a different problem this would only encourage.
- Describing things well, putting some thought into world building and just thinking through responses to player questions doesn't hurt either.
  Also, exactly which part of questioning the DM twice and sending a familiar in first was reckless in this scenario?
  And don't even tell me 'maybe they scrubbed the room after each time.' Have you ever seen a pizza stone?

I actually had the opposite experience as a DM, players were so paranoid and distrusting that I had to make the world harsher than intended so they wouldn't waste so much time being suspicious of nothing

I remember once session our DM got a new mimics minis set. When I say everything in the room turned out to be a mimic, I mean everything. The rug, the door, the table, the chair, the potted plant, and yes, the chest.

Should have kept the chest the only thing that's not a mimic!

Ah... familiar trap running. I am familiar with this sport.

A little too Raph.