Steve
Is the property empty?
Apply evenly all over, paying special attention to the edges, under tv units, side units, sofas etc( if applicable) as this is where fleas will lay dormant.
It is very important not to vacuum the carpets for 14 days as this period
is the life cycle of a flee. Any fleas that hatch after the application, should die. Then you or custy just vacuum them up.
Even if rentokil did the job, they would advise custy not to vacuum for 14 days!
As i said before, it may be necessary for a 2nd application so bear this in mind.
Steve