actually the offer is... the guy Offering to buy the car, The agreed value that the guy said he would sell the price does not necessarilly make it the amount he will sell it for.
You- How much will sell it for?
Him- $15000
You- I agree to the $15000 as requested by you
HE HAS NOT FORMED CONTRACT WITH YOU, MERELY SUPPLYING YOU WITH INFORMATION.
what you have done though is said youd by it on inspection of a mechanic at the agreed price. Right?
Which is a condition precedent.. and although it was only verbally done, a verbal contract is legally binding. now, you have gone through with your part of the deal which he has accepted, (assuming he accepted the condition precedent) which means he is binded to the verbal contract of the sale of car at the agreed price..
hope that helps..