The most accurate way to determine the value of your baseball cards is to have them professionally graded and authenticated. Professional grading companies like PSA, BGS, SGC, etc. will thoroughly inspect each card and assign it a numerical grade based on its condition and appearance. They will then authenticate the card to verify it is genuine.

Getting cards professionally graded is a service you have to pay for, but it provides a level of assurance that is very important when determining value. An ungraded card in questionable condition could be nearly worthless, but the same card receiving a high grade could drastically increase in value.

If you don’t want to pay to have every card graded, you can start by simply researching recent sold prices online for each individual card in your collection. The two best sites for this are eBay and PriceGuide.com. On eBay, use the “Completed Listings” filter to see what identical or near identical cards to yours have recently sold for at auction.

PriceGuide.com has a constantly updating database of recent online and live auction sales. You can search by player, year, brand/set, and grade to get a ballpark market value for each card. Neither site is perfect since values can fluctuate based on specific card condition or demand on a given day, but they provide a good starting point for common/identifiable cards.

For older, rare cards that don’t have many recent comparable sales, you may need to consult with an expert. Reach out to reputable vintage card shops, auction houses, or consignment services in your area. Send clear photos showing all four sides as well as any identifying printing information on the back. An expert can better authenticate it and provide their professional estimation of current value.

Once you’ve researched values, the next step is determining your cards’ conditions. This is crucial, as even minor flaws or issues can significantly decrease value. Evaluate each for centering (left-right and top-bottom alignment within the borders), corners (are they rounded or have nicks?), edges (wear along the sides?), and surface (dulls, scratches, marks?). Higher grades demand near perfect cards.

You’ll also want to note if any cards are part of particularly valuable sets, subsets, inserts, parallels, autographs, special editions etc. Parallel rookie cards in particular hold premium value. Consider having particularly valuable finds encased in professional protective sleeves and holders as well. Proper storage is important to long-term preservation.

With condition and value established, your options are to hold long-term as an investment, consign high-value singles/sets with an expert marketplace like PWCC or Goldin Auctions, or sell outright through a local shop, collector website, or your own online auctions. Be sure any agreement you make maximizes your potential profit – reputable sellers often charge commissions but can achieve the best prices.

The baseball card market sees constant fluctuations so values must be checked regularly. New findings or condition clarifications may change estimated prices. With patience and diligence in researching each step, you can properly assess what you have and maximize its worth. Let me know if you need any clarification or have additional questions!