Instructions
Shop local antique stores. Most of them sell old postcards. Thumb through all of the cards to get a feel for what appeals to you. The cards' prices will give you a good indication of their value. Pricing depends on a card's rarity and condition. Don't spend too much on your first card. If you find a Santa or Halloween postcard, jot down its price. These holiday cards are the rarest and most sought after.
Attend local auctions. Check your newspaper and the Internet to see where auctions are held in your area. Before an auction, the auction house will usually post on its website a list of items offered for sale. Some auction houses show photos as well. If you find an auction where postcards will be offered, go ahead and sit in on the auction. You have no obligation to buy anything, and don't worry---you can't inadvertently buy something you don't want just by nodding your head or scratching your nose.
Go to your local library or bookstore and peruse books on collecting vintage postcards. Many of these books list price ranges for the postcards featured. Make a note of the year the book was published, however, because prices are always changing. These books are mostly valuable for displaying categories of postcards and their rarity.
Surf the Internet but only after you've attended an auction or two, searched antique stores and read books on antique postcards. You are now more savvy and can spot a good deal. There are many sites you can join to find loads of information on massive postcard collections. One site is vintagepostcards.org. Join this site to receive newsletters and emails on news and events centered on the business of buying and selling antique postcards.
Shop on e-Bay, where hundreds of collectors sell antique postcards. The best auctions are those that sell by the lot. Set aside an evening just to check out e-Bay's offerings. If you're looking for seasonal postcards, be sure to shop before and during the season. For example, sellers are always selling Christmas postcards, but there will be many more Christmas cards offered in November and December.