Personal recommendation......or set up a webcam in your house to see what happens. I know someone who did this....the webcam was actually to monitor the dog to see if they barked when left alone....in fact it caught the “dog walker” doing just what you describe...even moving the lead and collar to make it look like they had walked the dog..AND they falsified the “dog diary”.
We have problems here with the walkers who take packs of dogs together. We were chased by one such pack and our own dog was attacked..the dog walker was off in the distance with no interest or control whatsoever, I would never use one myself.
We were lucky regards dog walking as my niece only lived five doors away and her son who was 15 at the time was quite happy to come round and walk Max.When I asked him why he replied "I like walking uncle paddy and you wouldn't believe the number of girls I've met,they all want to make a fuss of the "cute" puppy,"
My dog walker sends me video's of their walks and also she has a facebook page that she posts them on as 'advertising' for new clients.
She has on occasion said to me that she has when they have not been well taken them back to hers and let them run riot with hers in the field. I'm happy with that as they are still getting exercise and socialising with other dogs.