Buying from estates is something of a family thing. My Dad did several over his life, and both my brother and I have made one purchase from an estate. Usually we were purchasing lower mileage vehicles at a steep discount below book because others were afraid of the paperwork requirements. I found this "fear" to be unwarranted in my transaction, and the seller / executo was "happy" because I didn't back out or no-show during the process.
In 2010, I purchased a vehicle from an estate for about $7,000 under book value because I was able to pay cash (cashiers check) in full when I was provided all the required paperwork for title transfer. I did confirm the necessary paperwork in advance with the DMV / county.
Since the vehicle had been financed, the actual sale transaction was handled at a bank since they had to sign over the lien paperwork. The bank official handling the transaction was familiar with the executor and estate. The paperwork provided by the bank matched the DMV requirements.
Call the DMV or the title issuing authority in advance. If the seller isn't familiar with the process at some level, walk away. If you don't have to signatures notarized, ask to see a copy of ID to verify it is the executor signing the paperwork on behalf of the estate. You may to provide for return the certified estate documents to the executor. (I think I left the copies with the DMV and provided a return envelope, but I don't recall the specifics.)
In my case, the executor was a retired attorney settling the estate for a deceased friend. Additionally, the executor and I knew each other visually from over a decade of passing on the bike trails around town during my lunchtime rides. There was a high level of transparency, and the seller's information about the process matched the information from the DMV. Having a bank perform settlement added to the comfort with the transaction.