If you are looking to purchase a property, you probably won't have a choice with which agent you have to deal with, because you will be more interested in the property you have found that suits your requirements, although you may find several agents offering the same property.
During the purchasing process, it is much more important that the Abagado (Solicitor) you use, is one that you have faith in and who you are sure will deal with all the paperwork correctly. It might be worth considering any recommendations. The Agent will probably suggest his preferred Abagado, but beware, that recommendation might be to the Agent's financial benefit and the Abagado may not be good. If you can't speak good Spanish, make sure the Abagado can speak enough English. Lots of mistakes can be made through misunderstandings, and you may be 'lumbered' with them for as long as you own the property. Consider hiring the services of an interpreter if necessary if you feel you can't cope. It will probably be worth the cost.
Unlike in the UK and many other countries, a Spanish Abogado can work for both the seller and the buyer of the property (although this situation is gradually being frowned upon), so conflicts of interest can and do occur. Make sure the Abogado you choose is entirely independent, and is working only for you. Make a point of insisting that he does a good and proper search and that all the papers are in order. Many properties in Spain are not entirely legal or do not have the necessary planning permission, which is usually not the fault of the owner, but rather the many different authorities who often take a very casual attitude to the vast amount of paperwork they seem to generate, and often have differing standards when granting planning permission. There are new laws in place which put the onus on the seller to produce all the necessary paperwork to prove the property is fully legal, but currently, many Estate Agents still seem to be working around this law.
The purchase of a property takes about 4 weeks in Spain, and initially the estate agent will ask you for a deposit of about 10% to 12%. This amount usually includes his and the Abogado's fee.
The final stage in buying a property is for the buyer, seller and their Abagado's to attend a Notary's office, where the deeds of the property are read out to be sure everyone understands them. Many Spaniards, especially in rural areas cannot read. Naturally they will be read out in Spanish, so it is important to ask your Abagado to translate as the reading proceeds. If he cannot do this, you should employ an interpreter. When that task is complete, you have to agree to what was read out, and then you will be asked to hand over the balance of the purchase price (often in cash, unless otherwise agreed beforehand), and the property will be yours. Don't be afraid to question what you don't understand, or get things changed if necessary before you sign anything.
Next you need to ask the Abagado to arrange for you to be recognised as the new owner of the property with the local authority, electricity and telephone companies, and any other services that may be supplied to the property. You may also need to arrange for direct debits for these suppliers, and on receipt of your bank details, your Abagado will normally arrange this for you. If your property is in the countryside, you may have a well as your source of water. To use this it may have to be licensed with the local authority in your name. Of course, you can do all this yourself, but it usually involves a lot of hassle, especially as all conversations and paperwork will be in Spanish. Along the coastal areas of Spain, some Spanish people may have a smattering of English, but the further you go inland, there's much less chance.
Having moved into your newly acquired property, any external alteration or extensions you plan on building, must have planning permission from the local authority (and sometimes regional authority) before you start. Failure to do this may result in such work (and sometimes even the whole building) being demolished at your expense. Spanish people, especially in the countryside, usually build their own properties without any permission being sought (because that is what they always did in the past), but the authorities are cracking down on this and are very slowly catching up with offenders. Many Spanish people (especially in the countryside) still dismiss any ideas of getting planning permission as if it doesn't matter, but it does, and it could be to your considerable cost if you don't stick to the law. Another reason why you should be sure the deeds of the property clearly state that the property is fully legal. Because the owner of the property you are going to buy has a good position within the local community, it doesn't mean his or her property will be fully legal. Recently there was a case of a policeman building his house without permission, no submitted plans, no taxes or rates having been paid. The new owner was obliged to pay for planning permission, architects fees, outstanding bills, taxes and rates, extra solicitors fees, etc., all of which increased to the cost of the property by a very large amount, and with the potential possibility of planning permission being refused and the property being demolished..
Having found your perfect property which is fully legal, you may still have the problem of local or regional authorities changing or making new laws, which you obviously can't plan for in advance. A recent example was the Junta (council) of Andalucia, who out of the blue, decided that all buildings built within 100 meters of a river must be demolished (at the owners expense and with no compensation). This will involve tens of thousands of people to be put out of their homes, which in many cases was their life times savings. This problem is still in the process of being considered. BE PREPARED.