California zip codes out by LA and San Jose have been kicking eBay's PWE to the curb and returning everything or making the people who buy the cheap cards $5 for padded mailed delivery by refusing to deliver them. I have actually stopped using it for the most part on Dodger/Padre cards to prevent a majority of the traffic there since it happened to me twice in 3 weeks late last year. I've not seen that PWE non-machinable ---> 1st class package rule enforced elsewhere... yet.
Keep in mind, keep those non machinable envelopes less than the restricted rules for 1st class package enforcement. I had simple card savers non-machined getting sent back which was actually ridiculous and a few other choice words. I called their post office since the eBay buyer threatened to leave a negative on my account for doing nothing other than following rules and they said, "It's not going to be tolerated, and everything will be considered packages"... Like? Why setup a policy with eBay to use their system and then have someone dictate locally that they aren't going to accept that... What a bunch of you know.