How can we determine a cheap rim from a good one? It starts with the material, all steel rims are considered low end, aluminum ranges from low end to upper mid range. Carbon fiber would be the high end and only found on road bikes.

Examination of aluminum rims starts with the number of walls, single wall rims are weaker than double wall rims. Double wall rims have spokes in recessed holes, hence they should be easy to spot. Then we examine the manufacturing construction, some rims are pinned into place ( there may be hints on the construction by examining the joint ) and others are welded. The welded ones are stronger and preferable. Machined sidewalls are great for rim breaks, as they create a rough surface for the brake to bite down onto. The quality of spoke hole drilling is also important, low quality drilling that leaves sharp surfaces can lead to frequent flat tires.

The number of holes is another attribute of a rim, more holes means the wheel will be stronger but heavier. You will need the hub hole drilling to match the rim hole drilling. They don't need the same number of holes, but there must be a consistent pattern of skipping spoke holes for the two to be compatible.