How can I tell if my solar glasses are up to ISO standards?
if I had a pair of glasses, what would be the proper way of determining if they met ISO 12312-2 standards?


The process involves a lot of lab equipment, calibrated sources of infrared, visible light, and ultraviolet, and calibrated detectors. Extremely unlikely you'll be able to whip something up in your garage.

Buy from vendors with good reputation; these are online stores that sell nothing but astronomy equipment, and they know what they're dealing with. If you're an astronomer, you know who those are. If you aren't, go on various astronomy forums and see which vendors people are recommending. Or see the AAS page for a list of vendors.

Amazon is now cracking down on bad eclipse glasses, but realistically speaking they are not an online store specializing in astronomy, so their product vetting may or may not be perfect.

It's getting a little late now, so better hurry up and get your eclipse glasses already.

You can always dash to the local welding supplies store and get a #14 welding glass. It's completely safe and passes the ISO standard. Maybe get the whole mask to go with it, so your face won't get sunburned.