The first step is to do an inventory of the cards you have. Lay all your cards out and make note of key details like the player name, year, team, and card company (Topps, Fleer, etc.). Having a detailed list will make it easier to research the cards.

Once you have your inventory made, it’s time to start researching values. There are a few good resources to use:

Baseball card price guide books – You can find recent year books at card shops or bookstores that will list sales prices for most cards from the past few decades. Be sure to get a book from the current year.

Online price guides – Websites like BaseballCardPedia.com and PriceCharting.com allow you to search for sales histories of individual cards. They pull data from major auction sites to give a sense of what cards have actually been selling for recently.

eBay “Sold” listings – On eBay, you can search for a specific card and filter the results to only show “Completed/Sold” listings. This will give you a current market value based on what people were willing to pay for that exact card in recent completed auctions.

Ask an expert – If you have valuable vintage cards or one-of-a-kind cards, it’s a good idea to have them professionally graded and authenticated by organizations like PSA or Beckett. They can give an expert opinion on rare or potentially valuable cards. Card shops may also have experts who can evaluate.

Some things that can affect a card’s value include the player featured, the year and manufacturer of the card, the card’s condition or grade on a 1-10 scale, and whether it is part of a rare subset. It’s important to accurately assess these factors when researching prices.

Here are some tiers for cards that may be worth grading and selling:

Rookie cards for star players from the 1970s-80s era that grade PSA 8 or above could be worth $100+. Iconic rookies like a Mickey Mantle 1952 Topps in PSA 8 could sell for thousands.

Autograph or memorabilia cards for modern star players like Mike Trout or Shohei Ohtani could sell from $50-500+ depending on the card and player involved.

Rarer error or variation cards from the 1950s-80s era that grade PSA 6 or above could potentially sell from $100-1000+, with the most rare and high grade examples reaching five figures or greater.

Complete card sets from the 1970s-80s era that are in excellent condition could sell from $200-1000+ depending on the year, condition, and inclusion of key high-dollar cards.

Common cards of current stars in otherwise resellable condition from the past decade or two may have a resale value of $5-20 each.

After properly researching prices, it’s time to determine if your cards meet any of these value tiers. Any cards identified as potentially valuable should then be sent off to a grading service for certification prior to selling online through eBay or directly to a local card shop or collector. Proper grading significantly increases value, so it’s worth the $10-30 fee per card for valuable finds.

With patience and thorough research, it’s possible to uncover hidden gems worth significant money in old collections. Taking the time to properly inventory, research prices, grade key cards, and sell strategically online is the process to determine if your baseball cards are worth anything financially. Even common cards can hold nostalgic value regardless of prices.