The most accurate way to determine the value of your baseball cards is to have them professionally appraised. This involves sending your cards to a reputable third-party authentication and grading service like Professional Sports Authenticator (PSA) or Beckett Grading Services (BGS). These companies will thoroughly inspect each card, grade its condition on a scale like gem mint (GM/MT) 10 to poor 1, then securely slab the card in a hard plastic holder with the grade clearly displayed.

Getting cards professionally graded is recommended because condition is absolutely vital to their worth. Minor flaws or imperfections that aren’t obvious to the naked eye can greatly decrease a card’s value. Grading services have expert graders who meticulously examine each card under bright lighting and magnification. They will note things like centering, edges, corners and surfaces that affect condition.

After grading, the service will also provide a monetary value guide for the card based on sales data from recent auctions. Know that prices can fluctuate with demand over time though, so use the guide more as an indication rather than a definitive price. Still, having your cards professionally authenticated and graded gives buyers confidence in the condition assessment and will help you command higher prices.

If you don’t want to pay grading costs upfront, you can research estimated values yourself by first closely examining each card to evaluate its condition compared to sample photos online. Look at guides from PSA, BGS or price charting sites like BaseballCardPedia.com that categorize values based on the standard grades (1-10). Note the year, brand/set and any special variations that could impact worth. Some key factors that increase value include:

-Rookie cards of star MLB players from their debut seasons. Example: A PSA 10 Mike Trout 2009 Topps card could be worth thousands.

-Hall of Famer cards from their playing days. Example: A BGS 9 Hank Aaron 1954 Topps in high demand.

-Special parallel or short-printed serially numbered cards. Lower print runs mean higher prices.

-Promo, error or one-of-a-kind variations from the standard issue. Big collectors seek these unique pieces.

-Condition is everything. Higher grades (8-10) demand much more money than well-worn lower grades (5 and under). Even tiny flaws hurt value significantly.

You can then research recently sold prices of comparable graded cards on platforms like eBay, Heritage Auctions, or direct from PSA/BGS to get a ballpark figure. But understand prices can vary wildly depending on current demand in the marketplace. Also factor in costs to grade and sell/consign versus just keeping the cards.

Take your time carefully examining each card, research estimated values, then consider grading options if you aim to confirm condition and sell. With some digging, you may discover you have a true gem worth professional authentication and setting in a slab to preserve its condition and maximize its market value for years to come. Let me know if any part of the process needs more explanation.