I'm glad to know I'm not alone with the fingernail test, but sad to hear others are having the same issue (!).

I can still scratch the cheap stuff off fairly easily with my fingernail (digging in then pulling down), the industrial so far has been tougher but I can still do it.

There's probably still time for it to dry and harden more, but in any case I think it's unusual to have a sharp object dig in and scrape down, so I feel good (especially with the price) about painting a weekend cruiser car with it.