There are many ways around this.
First off, I'm never worried about buying a vehicle with just a bill of sale, IF the seller is reputable and can be found if ti goes awry.
Secondly, do not buy a vehicle if it is the lest bit hinky until it has had a police VIN check conducted to determine if it's stolen. If it's proven not stolen, obtaining a title is pretty easy, again, there are many ways to title a vehicle under these circumstances.
If it was totalled (and, some states have situations that require the title to be surrendered to the state to have a salvage title issued-Indiana does this for water-damaged vehicles fewer than seven years old) and partially rebuilt, if you can come up with receipts for the parts that were used to rebuild it, and an invoice for the rebuilding, you can obtain an "assembled vehicle" title.
Lastly, if you buy the vehicle and cannot obtain a title using reasonable means within 30 days (at least in Indiana) you can apply for several different titles through a mechanic's lien, garagekeeper's lien, or even an abandoned vehicle lien. There are folks who provide services to obtain these somewhat specialized titles, but I have found it to be amazingly easy to obtain a legal title for vehicles where the title was not forthcoming. It required a very limited amount of time and less than $100 to begin the process and when it was over, the only additional expense was paying sales tax and the titling fee-this is how I got the title to my wife's DII.
I have inadvertently bought several vehicles where the person who took the money an gave me a bill of sale were not in a position to do so. In every case, I was able to get a legal title with minimal hassle.
The title services make it seem hard to entice you to spend money with them for something you could do yourself if you knew how.
Bear in mind that a Defender with a salvage title or an assembled vehicle title will have next to no resale value. Buy carefully.
Yes, I am still alive, and still in the Rover parts business.
Text me for greatest likelihood of finding me.