You can check whether a holiday property has been registered on the Registro de Turismo of Andalucia, as it should be. So if you see one advertised without the registration number, and want to make sure you´ll rent a registered property, you can send an email to the Junta de Andalucia and ask them to check for you.
You need to provide details of the property (address), or the name and NIE of the ´titular of the explotación´ (in most cases the owner).
This is the email to use:
csu.ctd@juntadeandalucia.es
Alternatively you could visit the provincial Junta office to make enquiries in person there.
LINK to listing of offices.
The above information comes from emails with the Junta, they didn´t mention a third option, and that is to make enquiries at Town Hall of the town/city where the property is located. As all Town Halls should receive notification of all registered properties, once registration procedure is completed and they have been allocated their definite property registration number. Assuming they keep records that can be consulted.