well its always sth different if ur in kama n someone asks u about an item and u tell him some fancy made up stories for hours just to make him buy ur overpriced item.
But I think in general if u have listed sth on ur guru thread and u have a b/o price there for it, this doesnt rly say "oh that item sure is worth that much" it basically only says "I (the Threadowner) have this item here and chances are very very high that Id let it go for that listed price" ... Nothing else rly. So in the end its still up to the buyer what he then does with this information. If hes intelligent he tries to get informations about any item he (for whatever reasons) wants to buy, so if he finds an item he wants and the listed price is way more than he expected or is willing to pay he can just pm the seller and try to negotiate or just move on to another thread.
Negotiation how it prolly would go in the 10/10 case:
Buyer: Dear Seller, why are u listing a 10/10 mod in ur thread for 100e (or more)? Dont u know u can get it in a quest? Considering that fact, would u be willing to lower ur price?
Seller: Possibility 1: Dear Buyer, sry I didnt know that and I just rly want to sell it for a good price. Since I wasnt sure about the price I started high, but we sure can go from there and try to find a price that works for the both of us.
Seller: Possibility 2: Dear Buyer, I indeed knew about that, but I often need those kind of mods myself so Im not rly desperately tryin to sell here, just listed it in case someone needs one asap and cant find any other, so he at least then knows that I have one I could spare if the price was a bit higher than usual. I therefore recommend that u first look if u can find another seller who rly doesnt need the mod and would let it go for less.
Example of fraud for the same case would be:
Buyer: Dear Seller, u listed a 10/10 sword mod on ur thread with a seemingly high price of 100e. Why are u asking that much for it?
Seller: Well its totally worth that much, cuz its a rare prenerf Mod that cant drop anymore u will not find many others of its kind. U should be glad that Im not asking more for it.
Case closed