Just list his finances and we can tell if he one of them, like Pelosi, Clinton, Feinstein,etc.
According to this he doesn’t seem too “bought & paid for”, at least when he was in Congress:
“His last financial disclosure form listed assets worth no more than $606,000, and he had a number of financial burdens dragging him down, including a $300,000 penalty assessed against him by the House Ethics Committee for an improper book deal and a second divorce on the way.”
https://rollcall.com/2011/12/02/newt-gingrich-rose-to-wealth-through-congress/
Most of that net worth is explainable from book royalties and speaking fees, and not multimillion dollar ones like you see the usual suspects getting.