This is a great question and I'm sure you'll get plenty of responses.
A magnet will stick right through bondo, so this is NOT a certain way to know if it has body filler. Plus "bondo" is not nessesarily a bad thing, sure it has a negative stigma, but the truth is that ALL minor body imperfections are filled w/ some type of "bondo" (body filler) before its painted.
I've bought and sold 100's of cars in my life. Probably one of the biggest issues I have from in-experienced people, the scared paranoid type just itching for an excuse NOT to buy, is asking me (as the seller) a bunch of personal questions. This is a HUGE turn off, I just tell them I won't answer personal questions.
As a buyer, you either make the choice based on the merits of the car as it appears to you now, or not...just that simple.
So I strongly recommend against asking personal questions like "how long have you owned it", "why are you selling it", ....you're either buying it or not - based on the merits of the used car as you see it. The sellers personal information is none of your business, you're just a used car buyer.
You didn't answer a want-ad for date or marriage. These types of personal questions -and more importantly the sellers answers, do not add or take away value of the classic....they're just annoying questions. Personal questions to the seller is a HUGE turn off and not necessary to make a good purchase.
Cash. Time is valuable to everyone, buyer and seller. Have CASH in your pocket and a good attitude. Nothing worse than someone "looking" without having cash in their pocket.....you're not a serious buyer, never were, and never going to be unless you have cash. No checks, no delays, no trips to the bank, no excuses, no BS...you're either a serious buyer, or your not.
Buyers remorse. Often when people pay X amount of money for some glorified toy later they feel bad, buyer remorse. Make up your mind and stick w/ your decision. Never allow yourself to feel bad because someone else *thinks* you paid too much for a classic. Life is short and precious, money comes and goes in life....but classic cars make you smile
Most old Bronco have been modified, many of them have been modifed several times. Often by people who are self-taught and learn as the go as a hobby project. If you're not an experienced mechanic, contact an experienced mechanic and have them go with you. The dollars you spend on seeking quality advice from an experienced mechanic will pay you back in spades in the long run.
Everyone has their own little quirks, wants and desires when shopping for an old Bronco. I'm at a stage in my life where junky cobbled together mechanic work and modifications is something I'm just NOT interested in dealing with. Nothing worse than fixing the original issues w/ old cars, plus having to fix someone else's previous mistakes.
And personally, I'm not into rust...I just don't do rust. And because I won't buy a rusty classic -unless it's some really special classic, or a previously worked on project, the overwhelming majority of classic Bronco's are not for me. I'm so picky, that when one does meet my criteria the price is very high.
Best wishes sir..........