I thought of another couple of simple 'signature' tests you can do with the 10073C probe if you have access to an ohmmeter.
Measure the resistance across the BNC connector at the scope end of the probe. Don't connect the probe to anything else other than the ohmmeter.
Two of my probes show 287.7 k ohm in this test.
Then, keep measuring the resistance and then press the little orange ground button on the probe. This tiny button is on the tip section.
With this button pressed you are now probably measuring the series loss resistance through the coax cable. My two probes show 376 ohms and 378 ohms in this second test.
This isn't a definitive test, but hopefully you will see similar resistances with your ebay probe?
