Among other due diligence procedures (your solicitor/lawyer will help you with it) you MUST write a letter to the condominium administration to find out if that particular fraction of the building (the apartment you intent to buy) owes any condominium fees to the company who manage it.
Just for your information a buyer recently had to pay close to 5.000,00 in condominium fees owed by the last tenants (the debt does not belong to people but the apartment/fraction of building which can be a tourism villa inside a tourism development or others).
Take that in mind next time you try to buy a property in the Algarve with this characteristics.
All the best!