Is there a difference in quality between the two
(hacked database vs spammed)?
I think he is reffering to the fact that most people spam crappy emails they get from shitty crawlers and all
Somehow, emails comming from hacked websites SQL, are not so widely spread throughout the web because hackers wont sell for small prices like $50 per 1million.
You can easily tell if they are good by simply asking for 500 pieces sample, spam them with your email as reply-to and see how many mailer-daemons come up
If its more than 2%, its probably a shitty base anyway or old to say the least, hence sometimes called spammed emails / overused
Any seller refusing to give you such small samples ( or request small payment for them ) so buyers can test validity, shouldn't be dealt with in the first case.