You may want to think twice about having your items valued by the person who will sell it unless you already have a good relationship with the seller. An unscrupulous dealer could easily mislead you as to the value of your goods. A dealer can tell you that an item is worth little when it is actually worth a lot of money. Of course, most dealers are not crooks, but business is business.
An appraiser can identify and value your old pieces. There will be a fee, so you want to be pretty sure that your things have some value. You can learn a lot about your goods yourself before you commit to an appraisal that will cost well over one hundred dollars.
Then you can move on to a dealer. Of course, a dealer will need to cover his own costs and make a profit. So you can not expect to make the full value of an item if you sell it to a dealer. The same goes for consignment. Expect to part with about 1/3 of the sales prices if you sell on consignment.
You can find an appraiser by checking out the American Society of Appraisers or by contacting your insurance agent.
If you don't already have a relationship with an antique dealer, ask around. Ask your friends, relatives, and neighbors if they know someone you can trust. A dealer might not buy everything you have even if it is valuable. They will buy what they think they can sell. If your goods are fine antiques, or quite valuable, you will want to deal with someone who specializes in fine antiques. There are many kinds of dealers out there who specialize in all kinds of things - dishware, furniture, artwork, primitive, European or Asian antiques, etc.