Before you buy a second-hand property in Poland, you should definitely:
- obtain confirmation from local authorities (Urząd Gminy) that no one is registered as a resident in this property
- check if the property has any debts (e.g. unpaid bills), which you can do at the spółdzielnia mieszkaniowa (home owner's association)
- check if the property is recorded at the land registry (księgi wieczyste) and find out whether it is mortgaged (everyone has access to the land registry)
The land registry defines who has the right to sell a property: If you buy your property from the owner indicated in the land registry's records, but in fact he's not a legal owner, don't worry because the property is yours.
Apart from legal checks, you should also do a detailed check of the property condition. Pay attention to wiring, piping and gas installation, the condition of plaster, and the state of the windows. You should hire a nadzór budowlany (building inspector) for this job. If you are buying property which is older than 50 years, using a nadzór budowlany is actually indispensable.