Protect yourself further with a signed contract between you and the seller
There needs to be a degree of trust on both sides in any transaction, but the stakes are higher than normal when buying a used car so you need to protect yourself as much as possible. One way of doing this is by asking the seller to sign a contract – whether they're a trader or a private vendor.
The contract here is self-explanatory. Suffice to say that if a vendor isn't prepared to sign it before they sell you their car, they clearly don't have much faith in it – so why should you?