Are offers by buyers binding?

Until they put the money in your hands you are free to do what you want. If they come see the car and put down a deposit you should honor your agreement. If it is just an e-mail I would use my judgement as to whether they are serious or not. It is your call.

Verification by CarGurus, not by the seller.

You don't have to respond if you don't like what I'm asking.

Tom is just trying to point you in the right direction.

No offer is binding unless either money changes hands or there is a signed contract. As Tom told you, use the contact us button at the bottom of the page for answers to questions like that.