I know there was a way to get Franko to give you nearly everything for a single item before the 1.2.2 patch and now he much harder to trade with. One thing that I think needs to be corrected or changed is if I have a single diamond or bandage he will say that it is exactually what he is looking for and it is worth a lot. My problem is that if I have more then 1 of that item he says it is very common and is almost useless for trading. I have tested this by not taking more then 1 diamond from a location, snipers alley, and the next day he will give me a large credit for trading. If I take all 5 diamonds from the location he will not even sell me 10 water and 4 gears for 5 diamonds. It's not just the diamonds but anything I have in my inventory if I have more then 1 it is very common and he is not interested in it. I haven't tried to see if this applies to all trading characters though but it might be the same.
Is this what you wanted? How should he know that I have 1 or 100 diamonds or any items. If I have 1 of something that he says is the highest value to him then why does it become near worthless if I have more then 1?