If it's cosmetic or superficial damage, such as from scraping a curb, the wheel is probably still round and has no bent sections or chunks of metal missing. On the other hand, if the wheel is bent, cracked or structurally weakened from hitting a massive pothole, running over a steep curb or some other mishap, it may need to be replaced, though it could possibly be repaired.
A dented wheel may not be able to maintain a seal with the tire bead, resulting in consistent slow leaks or blowouts, and will be difficult if not impossible to balance so that it doesn't vibrate at speed. A wheel with structural damage could eventually break apart. When in doubt about the severity of damage, a mechanic experienced in assessing wheel damage should inspect the entire wheel with the tire removed.
Whether to repair or replace a damaged wheel is often a judgment call, but because it involves safety issues as well as cosmetic concerns, the best course is to err on the side of safety.
Repair services that promise to restore badly damaged wheels to like-new condition might be able to remove dents and bends and make a rim look great again. However, there are no federal safety standards that apply to refurbished wheels, so you'll be taking your chances as to whether they'll still have their original strength and integrity.
Repairing more than superficial damage will not be an easy do-it-yourself project. Heat and specialized machines are used to straighten bends, and a complete refurbishment involves removing all paint and protective coatings, repairing corrosion and physical damage, then applying new coatings.
The cost of repairing a wheel will vary by size, type and amount of damage, and it might approach the price of a new or used replacement. Many original-equipment alloy wheels can cost hundreds of dollars (even thousands in the case of luxury and sports cars) to replace, so buying a used one can save money. However, it might be hard to determine if a used wheel had prior damage and is refurbished.
