The following is an oversimplification:
When deciding to sell sports cards, you may want to get some or all of these cards graded. In the modern marketplace, it makes them more liquid (easier to sell) and often causes them to sell for more money than their raw (ungraded) counterparts. This difference in price is a key part in determining which cards to grade.
If you're reasonably accurate with grading your own cards, you can help yourself by doing the following:
- Determine the condition of each card, on a 1 to 10 scale, using PSA guidelines.
- Take that number and lower it by 1. If you think your card is a 6, call it a 5 for this exercise.
- Find recent "sold" listings for copies of the card you're trying to sell.
- Isolate those sales for copies of your card in the PSA grade (use that lower number.) Average the last 5 sales of cards with the same general qualities (especially centering) as your copy. That's roughly what your card is "worth")
- Repeat the process for raw (ungraded) copies of the same card.
- The difference in average sales price is the value you'll add by getting it graded.
- Cards with the largest differences will make the most sense (financially speaking) to get graded.
These are just steps I would follow. Your mileage may vary. No guarantees, of course. Grading companies can do some bizarre things, as can the sports card market.