The type of ink you use makes a huge difference on how well the image turns out when using clear stamps. Also, the material the stamp is made of affects the image - photopolymer stamps work the best, but I've use all types and can generally get them to stamp cleanly by using the proper ink. Pigment ink works best with clear stamps. I particularly like the Studio G inks for stamping with the cheap clear stamps. I also like Colorbox & Versa Magic - they work really well also. The pressure you stamp with affects the image too. The non-photopolymer stamps most of the time will be more squishy, so you have to have a lighter touch with them otherwise the image gets distorted and blurred when stamped. Most times, I don't have to "season" the stamp (using the eraser or sanding block) if I remember these things and adjust for the stamp characteristics. I use seasoning the stamp as a last resort to get the stamp to accept the ink evenly (I've even had to do this to rubber stamps). If you're trying to use dye inks with clear stamps, you can try coating the image with Versamark first and then into the dye ink. I also discovered by accident if you stamp in ink and let it dry on the stamp (with Stazon or a hybrid ink) the stamp will then take ink better too.
Hope this helps...