Has anyone ever dealt with lice or fleas being brought into their home (by a client dog)?

Fleas have been discussed many times in the Q&A section, but I haven’t seen anyone discuss lice on this forum. The best way to avoid flea implosion is to have a firm policy that all dogs are on an acceptable flea prevention treatment before they come to stay with you. In cases when the flea prevention method has failed, a sitter could contact the owner to authorize a vet or groomer visit to remedy with appropriate bath or RX. Even then, an outbreak is possible. For those who don’t want to resort to using heavy chemical bombs, the after the fact remedy is extremely time & labor-intensive with washing everything in hot soapy water and vacuuming constantly to break the cycle.

If your dogs were on flea prevention and the visiting dog was not, it might be easier to have convinced them that a tip upon their return, in an attempt to partially compensate you would be appropriate. However, your profile mentions that the dogs go out in your yard without you and you take them to places where dogs can hike & swim. In those natural environments, which have untreated wild animals (rabbits, squirrels, etc.), It’s much more difficult to determine source of lice or fleas. Hitchikers could have been picked up/ landed on any dog while not under your direct observation and then brought into your home.