Wish there were a simple answer to that question !! But glassware is so expansive a subject that it would take an entire library !! Is there a classification of glassware you are most interested in ?? Like Milk Glass,,Depression Glass,,Art Glass ect ?? And are you intending to purchase for resale or to keep ?? If so you can buy reference books that will help somewhat for identification purposes !! But the very best reference for what is a fair price to pay and is easy to use is Ebay !! If you see something you are interested in just look it up on ebay That tells you the asking prices,,both high and low and if there is interest in it !! Of course there are always a few that will have sky high prices so disregard those !! Stay with the low and middle end prices,, see who has bids or watchers and if there are none then look to the lower price !! If there is some interest from the buying public then add a few dollars !! Just use common sense !! And another thing,, with glassware do not buy if it is chipped or cracked no matter how cheap it is unless you are going to keep it for yourself !!
If your hand held computer/phone ect will do it,,not all will,, when you look at an ebay page in the left column you can see completed listings and sold listings !! Click on the sold listings and that tells you what people are actually paying for an item !! Use your home computer to see what I mean !!
I am glad to answer any questions you may have !!