The purchase contract for a resale property will contain details of the vendor and purchaser, the purchase price and method of payment. It will also confirm that the Escritura de Compraventa (Title Deeds) is in the name of the vendor and that this will be passed to the purchaser on completion of the sale.
It will also guarantee that the property itself will be transferred free from all encumbrances and rights of third parties and will state who is liable for taxes and costs involved in the transfer. There will also be stipulations regarding penalties for non-fulfillment of the contract.
The purchase contract for a property still in construction will contain similar details and normally further information regarding ownership of land, building permissions, completion dates and the setting up of a community, etc.
Often contracts are written in English and sometimes they are in Spanish with an official English translation. Your estate agent should go through the contract with you and clearly explain any details that you do not understand. If you are not sure of any clauses in the contract, or have doubts about the fairness of the stipulations in the contract, then do not sign it.
You can still pay a holding deposit to secure the property and let your legal advisor vet the contract before you sign. As stated earlier, no reasonable developer will refuse to refund a holding deposit should a solicitor find any legal reason why you should not proceed. Good estate agents will only deal with reasonable and reliable developers.