Tf2 and validating mandating to
I get the some problem when I try to run games that I store on my ext3 drive (accessed via 3rd party driver), indicating that Steam seems to make quite low level system calls to check files.
You will just have to deal with it till Steam updates to deal with the new FS specs. My suggestilon would be to try deleting the TF2 game cache and start again.
It compares the game files you have on installed your computer with those of of the latest version on the steam servers.
If someone tries anything listed in the above points, don't try to trade anyway.
The people doing this are usually professional criminals who do this for a living, and have been doing it for years.
No matter how stupid they seem, or how great the deal looks, the only thing they are really interested in is getting your item(s) for free by tricking you into doing something unsafe before the trade.
There are no "Steam admins" who get involved in trades either, and if you do what they say you'll lose your items.
Please confirm who you are dealing with any time someone says they're an admin: https://steamrep.com/tips/pretrade.