How do I find the re-sale value of collector items from Bradford ExChange, San Fran Music Box Co, etc?

My parents ped away, and I have a rather large collection of items they purchased from Bradford Exchange, Franklin Mint, San Fran Music Box Company, and a few other companies. I wouldn't say the items are antiques. I do know some are well over 10 years old. My mom collected Gone With The Wind pieces, and my dad collected Elvis Presley. I have started to research some. I started on eBay, and I didn't see any of the pieces that I have. Some of the items came in collection of 6 or so {I have the entire collection of many sets}. I have tried some on-line research, and it hasn't been very successful. I need to know what to do. If I have a rare piece, I would like to KNOW that it is. Where should I start? Should I use a seller? How do I know if they are a respectable seller? Would I get more money if I sell them, versus letting someone else?