A question for people who have done direct marketing: is it advisable to email prospects taken from email lists purchased from mailing list brokers/compilers?

I have been told that the direct marketing message being considered as spam is a big problem with such a source of emails (the commercial mailing list). I was also told that the accuracy (for delivery) of the lists that are purchased is only around 60-65%.

I would like to hear from people who have actually done such an exercise. How did your email outreach program turn out?

Would you recommend buying an email mailing list from mailing list brokers or compilers? Any pointers on what not to do?

thanks.