To form a valid contract, three elements must always be present:
1. An offer ;
2. An acceptance ; and
3. A 'consideration' (i.e. money or some other type of payment)
So, for a contract to be created, a deposit would probably need to be paid. Even if it was, and the vendor then withdrew his/her offer to sell, there's little that the potential purchaser could do other than to demand his/her deposit back.
There might be an exception where, say, the potential buyer was a film company requiring a very specific type of car to be used in one of their productions and where (because the vendor withdrew his offer to sell) that company subsequently lost loads of money through having all of the actors and crew on set but with no car for the filming to take place. Under such circumstances, the film company might well be able to successfully sue the vendor to recover their losses.
However for Joe or Jemima Bloggs, who's simply been let down by the person who he/she thought was going to sell a car to him/her, there's no practical recourse available to them.
As PP wrote on your original thread, the situation is not dissimilar to someone thinking that they've agreed to buy a house, only for the vendor to then sell to someone who makes a late (higher) offer. It happens hundreds of times every day, often leaving potential purchasers out of pocket through, say, having paid for surveys on the properties but there's little that can be done about it.
A possibly relevant thread:
https://www.honestjohn.co.uk/forum/post/index.htm?t=62907