Referring back to post #8, I think what you are seeing is inaccuracy near the end (or beginning) of a cut. For example, when using a rip fence, you don't have quite the same control at the ends of a cut as you do in the middle. Some of the solution is simply experience. Be sure the fence in- feed and out-feed are long enough and the blade is parallel to the fence. Many saws have adjustments, and I use a dial caliper to set mine. It often means loosening the bolts that hold the saw arbor/motor unit to the table top to get it right. That adjustment does not need to be done very often, but I would always check a new saw to be sure it is in adjustment. Blade wobble can sometimes be addressed with blade stiffeners on both sides. If the arbor is bent, that is a much more difficult, but not impossible problem to address.
One hint is to not saw completely through the PCB. Go about 3/4 of the way through. That allows better control during the out-feed or end of the cut. It also keeps chips of PCB from flying at you. The piece can the be snapped and the flashing easily removed. As for the error in the shorter cut (i.e., a cross cut). The trick there is to be sure your miter gauge is adjusted correctly and the PCB is held tightly against it during cutting. I would not try using the ripping fence for that cut.
When I mentioned cleaning the edge with abrasive, of course, you need to keep dust to a minimum and wear a particle filter to cover your nose and mouth. For just a few items, the abrasive paper (use paper intended for metal finishing or "wet or dry" paper) can be attached to a flat block of wood. I also use metal abrasive strips impregnated with carbide. For higher volume work, I would use a belt sander/grinder, not a bench unit with wheels.
In sum, I think adjustment of your saw and careful technique will suffice. I rarely have to do more than touch up an edge. As mentioned by FVM, purpose-made shears are an excellent option. Be aware that PCB material is quite abrasive. Paper shears will likely dull quickly. Even metal shears will lose their edge. A prototype shop I am familiar with had two foot shears. One was for metal and the other was for PCB's. No one dared use the metal shear for a PCB.
John