I wish I could be comfortable doing so for such a large purchase, but there is too much variability in the quality of used vehicles and sellers have a disincentive to disclose potential issues.
I don't like buying at dealerships but I do like being able to inspect the vehicle at the same time I am signing the paperwork.
Carvana has 7 day return policy no questions asked. Buy it, take it to mechanic. Return it if its no good