The main thing to do id check with their other customers and ideally if there is soembosy that lives locally to the property to also them keep a eye open
On urbanisations the word normally spreads quite quickly who are the good and bad guys
You should ask them to produce paperwork that they can prove that they are a legally registered with the required insurances
Thde other big problem is price for services, if you are not paying tax and NI it´s easy to offer what would appear to be a well priced service so if you are unsure ask to pay for 3 months first
Obviously putting somebody into a property without the owners permission could actually be seen as a criminal offence, if of course you could prove it
I would hope that you have now changed the locks