You, the buyer, signs it. Usually the dealers won’t sign these, therefore it’s not a mutual agreement.
That is just wrong, though the words in it matter to how binding it is on the parties.
A contract is a agreement between consenting parties which requires offer, acceptance, and consideration.*
A purchase agreement is a contract (of adhesion) in that the dealer made the offer (that written document that probably says "agreement" at the top), the purchaser's signature below the line that says "I agree..." is acceptance. So long as there is consideration, like money in exchange for a vehicle, that makes it a contract.*
BEWARE! It probably says the dealer has the right to change the terms of the contract, but that doesn't mean it is not a contract.
It would be very hard to argue in court that the document the dealer printed as a "contract of adhesion" and handed to the buyer after a negotiation and verbal agreement was not an offer, with an intent to enter into a binding contract.*
Granted, there are eight defenses to contract,* but that agreement is a contract on the part of dealer.*
*this is not intended as legal advice, but only an opinion, though absolutely correct, by some yahoo on a truck forum.