I have an album of those rare cards that I wish to let go at trade fair later. Please teach me

Hi all,

Im visiting the expo fair later and I had never done before (all cards I pulled myself) I search in price charting if psa 10 or black label can go extremely high value. I see myself (if im not wrong) some of them is psa 10 quality.

Im visiting the expo fair later and I want to ask if vendor wants to buy my card.

But how should I deal with them? Like approach every stall n ask them can like this? Or its not allowed? Then, if they offer me the price is base on raw price right ?

Thank you all buddy here who's going to teach me. I grateful to it.