There are no more pitfalls than using an agent, infact some agents lie more than owners,(they are doing it every day 😉 ) I have bought and sold several times in spain and about 10 years ago if a seller put a property on the market through an agent the agent used to ask to see the escritura in order to forsee any problems. This has not been the case for the past five years or so. Clearly then the agents do not exactly know what they are selling so the difference between a private sale and an agent is nil. Infact you may get a better deal, I sold a house privately and gave a substantial reduction because I didn’t have to pay the 5% (plus IVA) to an agent. Do get a lawyer though.