The costliest error remains using the agent's recommended lawyer. The seller gets a commission only if the sale goes through, which differs from protecting the buyer. Your own legal adviser costs a fraction of what is at stake and is money well spent.
Signing documents you cannot read comes a close second. A certified translation costs little next to what is at stake. Promises made in conversation mean nothing if the written contract says otherwise — only the signed text matters.
Purchasing off-plan on trust has wrecked a great many buyers. Before any payment, examine what the company has already delivered, the building permits, and the guarantees on staged payments. Projects running behind schedule are common even with reputable builders; stalled projects are less common but far worse.
Forgetting about resale is a quieter mistake. Any property will one day be sold, pluzine real estate and the resale market matters. A property for sale in gazipasa attractive only to a narrow group is harder to move when sentiment turns.
Lastly, many buyers misjudge the running costs. Local tax returns may be required even when the home sits empty, and overlooked notices attract charges that grow over time. Arranging a local tax adviser from the start prevents most of these problems.