How much you believe them is probably a good proxy for how important you think campaign finance issues are.
Except I've never once seen such a claim actually made by any politician. So at the very least it seems likely to stand out.
And as for how to believe them: "I intentionally have no access to the donor list, I have never seen the donor list, and if you tell me you've donated to my campaign I will have no particular reason to believe you, so don't bother".
Marco Rubio made a claim like that on Meet The Press two days ago.
> I intentionally have no access to the donor list
That would require doing away with the $50,000 per plate fundraising dinners.
I've seen it made by almost every politician I've seen questioned about the impact of particular donations, and most people defending campaign donations against proposals to regulate them more closely; and as a lifelong political junkie and Political Science major, those are things I've seen quite a lot of.
As an opportunity to talk to me about an issue? There'd be far better channels for that.
> Or figures out what sports game you're going to, and pays to rent out the entire row of seats next to you. Or pays to do the same for your staff - who advise you?
Then I'd be very interested in how they managed to break my security and privacy, particularly to figure out what seat; that just seems more creepy than anything else. And it seems more like something you'd do to a candidate you don't want to see elected, considering the PR image it would project.
(Also, do you mean "rent out and leave empty" or "rent out to fill with people who want to bug me/them"? Either one seems obnoxious; the first is wasteful and creates an awkward situation, and the second seems decidedly creepy.)
If you want to talk about strange things people with money can do to campaigns, there's the whole "third-party campaign ad" thing to talk about. Whether you're doing it to support a candidate or to attack one.