[obsurveyor]

Assuming you got paper glasses, on the inside of the arms of the glasses should be information about the ISO certifications and who manufactured it. Compare this against NASA's approved manufacturer list. If there's no info or they're not on the list, don't risk using them.

It's weird but I've got a co-worker who bought some cheap Chinese ones and actually block more light from a phone's flash LED than my legit, approved pair. I'd still never use them since my test is very simple and I don't understand enough about the properties that make for good solar filters.

[tantalor]

Wouldn't a faker just steal the name of a manufacturer on the list?

[obsurveyor]

As far as I understood, the "fake" part of these fake eclipse glasses is calling them eclipse glasses with the implication that they are safe when they are not or not made to the proper standards, not that they were forging real manufacturer information.

[sbov]

Your understanding seems wrong: https://www.eclipseglasses.com/pages/safety

If your understanding were correct, the difference between fake and real glasses wouldn't be minor ones such as round-ness of certain parts.