A perennial concern is the problem of people posing as official callers who then distract you at the door and see what things they can steal.
Recently we have heard that a caller is posing as a "Water Board" official and wants the person to run water. Severn Trent officials would always introduce themselves from the company.
So the advice as always is be suspicious of any unexpected callers, check for ID, and if you are not comfortable, ask them to wait while you ring their company to confirm their ID. A real employee will be happy to wait while you do this.