Direct Mailer source for leads list

[Melvin M.]

I'm currently compiling a list of homeowners to send a mailer out to. I've looked at list source and DataAxleUSA. What I don't understand is they can "sell" me access to this list they have, I can take the names/addresses off to use for my mailers and place into my own database, and yet they're saying if I use their list that I'll be charged $500 each time. How is that possible or even legal if I'm pulling names/addresses from their excel list they send me, transferring the ones I want into my own excel spreadsheet and them using them in conjunction to the names I have already. Are they "bluffing" about their auditors being able to track that list? I understand their premise for wanting repeat business and controlling the list, but how is that remotely legal for them to claim the names/addresses they have (which I believe are accessible to the public) can be "owned" by them. Any help and recommendations are greatly appreciated. Thank you.