Well, IMHO, they are truly moronic salesman if they let either factor inform their treatment of you, and to be honest, that would tell me all I needed to know about that sales person, too. Find another salesman or another dealer.
On the "shifty" front, being "shifty" doesn't mean you aren't interested in, and can afford, a new car. Look at City banker types. Or drug dealers.
As for the 100k mileage, I deliberately tend to do that. I went to a BMW dealer in a 10-year old Granada with 120k on it. Ordered the new M3. I also tried an Aston Martin, with the same Granada. They gave me the keys to a DB9 and asked me to be back by closing time, some 3.5 hours later. I was back in 30 minutes.
Sales people clearly DO have to try to qualify potential customers, because spending too much time with tyre-kickers is a waste, but if they're doing it on superficial criteria like your current vehicle, they're seriously daft. Any decent salesman knows that appearances can be deceptive, and that people that don't look wealthy sometimes are, and that those that do look wealthy, sometimes aren't.
You show up in that 2-year old high-end Merc, you could be taking your bosses car to the carwash. You show up in a 10-year old Granada, it could be a cheap run-around. You could also be a successful self-employed person that doesn't use your Ferrari to go to clients because it's too ostentatious and will cause them to think you're overpaid, so you use a comfortable, but old, run-around .... which is what I was doing, except that there was no Ferrari.
Oh, and on the subject of Ferrari, I did have a test years ago of a 308GTS, having showed up in some similar old clunker to the Granada. I think it was a Rover V8. They didn't bat an eyelid, treated me courteously, professionally and as if I were serious .... which I was. However, nice though it was, I decided that it wasn't nice enough to justify the cost, and the running cost, over more sensible but still very nice cars.