It's fine to test them with lab equipment, but a complete check should include the various devices they are intended for, in various conditions.
Here are more suggestions, off the top of my head.
Check for tarnish on the contact points, however this is done. Put it under a microscope, or test resistance with an ohmmeter.
Find out what substance (plating, etc.) is on the surface. You don't want galvanic corrosion as it touches contacts made from a reactive substance.
Find out if certain contact shapes are less liable to gather dust and dirt. Some shapes may even be self-cleaning with each use.
Try every which way of inserting and removing them. See if metal fingers bend or break or get misaligned.
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Conversely, is there any way the adapter could ruin someone's device? Cause misaligned fingers?
Examine metal fingers under a magnifying glass. Is each of them one piece of metal? If made from two pieces, are these soldered so that no bad contacts can develop?
Does the plastic housing break apart easily?