I view buying old cars from any source as a risk, no faith involved. There are things I won't know and can't know going into the transaction, and I consider the risk/reward ratio of the situation. I evaluate if I'm ok with losing a certain fraction of the money I'm putting into the deal because of the unknowns.
I bought my '80 FI off of ebay based on a information from the auction posting and discussion here on the xweb. See
https://xwebforums.com/forum/index.php?threads/black-1980-x1-9-on-ebay.33641/. I also had a PM with the member that went to see it in person and that info was valuable too. I set my ebay bid based on what I thought the value of all the parts the PO had put into it plus the inherent value of the x itself. If I got it great, if someone else did, that's fine too. My point of comfort was that I was ok with the risk/reward ratio of what i was getting into.
I bought my '74 off ebay too. Not that ebay is my preferred venue, it just worked out that way. It was another situation of watching xweb for info and making a risk decision. Here is the link to that thread.
https://xwebforums.com/forum/index.php?threads/74-x-on-ebay.32662/#post-277016 Most helpful to me on that buy was that the x was less than 30 miles from my house so any transportation logistics costs were eliminated. There was some back and forth in the thread about paint and rust and so forth, and I just figured for the buy-it-now price in the auction, I could part the thing out and be OK dollar wise. So I took the chance and it's been a nice little car. Not perfect, still has a lot of issues, but on a cool, sunny day, it's a great place to be.
I don't have enough money to risk on a deal with a major auction house. With all the fees and costs, they are all out of my league. But that has not stopped me from enjoying the old car hobby.
There are no guarantees with these old cars, Fiats or otherwise. Buying one is always a gamble at some level, so you do your best to minimize your risk and then you take your chances. Xweb is a GREAT place to gather information and advice so you can drive down the risk and put yourself in a comfortable position when you buy (so thanks Xweb) but you can't be afraid to take your chances. Nothing ventured, nothing gained. At some point, you just have to go for it. And that is part of the fun.