Dr. Matt has a video on what he calls the tap/wobble test.



Very few razors are perfectly straight and flat; but only a few are seriously warped. Most razors can be honed successfully using various techniques, but if you are a beginner, some of these techniques may be above your current skill level. Thus, you may want to develop your honing skills on razors that are nearly flat and send out any with significant warp/wobble to some who hones hundreds or thousands of razors a year. That will save you a lot of frustration. Once your basic skills are in place, you can tackle more difficult razors.