Memorabilia cards with pieces of jerseys or equipment worn by athletes are great, but it's a mistake to think they are automatically valuable. Products released in the past few years have flooded the hobby with single color jersey swatch cards, many of which are a tough sell.
Jersey cards from 1999-2000 have held some value because they were still a new phenomenon back then. For newer memorabilia cards, you want to look for swatches with several colors of material visible - often called patch or prime swatch cards. Collectors are sometimes willing to pay a premium for especially intricate or unique multi-color swatches.