When I bought one of my houses the seller told me 'Everything legal' repeated this a couple of times, this did raise some suspicion as to what he was going on about, anyway I wanted this house, deposit paid. solicitor set up, same one as the seller but she made it very clear under no circumstances was she working for the seller in any way, and told the seller this in front of us both, all went well up to the day of paying and signing over, my solicitor went though everything once again to make sure we understood what we were buying.
Now it came to the part of 'Everything legal' from the seller, she said your'e buying a house and garden, no garden I said, the seller had built a double garage in the place where most of the garden had been, pitched roof, water, electric, the works, so now we are in the Notaries office and all hell is let lose between the seller and my solicitor, with the seller coming out to me explaining yes the garage had been built with no permission but Spain had a law that if something like this was built and no one complained within 6 years then it stayed...No idea if this was true and don't care.
Paid the money over, moved in, also part of the large upstairs balcony had been glassed in with doors front and back which we converted into a dining room, sun room, never a mention of this from legal people or on the deeds.
I sold that house and told the agent about the garage, she asked me if I wanted it put on the deeds, not if the buyer isn't bothered, no I said, had that house for 10 years and not one problem ever arose over the garage or the glassed in part.