Well, I am not on any of those type of platforms, FB, IG etc. but if the price is too good to be true, if a US made product is being shipped from China etc. and so on. Do your homework. If it were me I'd look around the exchange here for some members with good feedback or look for an authorized dealer.
If the knife is far cheaper than can be found elsewhere, there may be a reason for that, possibly a bad one. If it is just something rare and you must have it, then I guess you have to roll the dice. Again, good luck.