If you ever come across any times that appear to be glitched(flashing/messed up graphics), don't keep or take them. I haven't personally heard any signs of this corrupting anyone's save, but it's better to be safe than sorry. Even if they were harmless, you can't un-glitch them. Otherwise, they are safe.
If you happen to want to look for these items outside of TBT, please get help from someone you can trust, as you would with any transaction. And don't interact with someone who's asking for in-game items or real money...they're trying to take advantage of you and others.