Experts and BHG readers answer.
Springtails like damp locations. Could there be a slow water leak under the sink? Perhaps a damp spot along the foundation? If the home is vacant, turn the water off. Rake away any decaying leaves or mulch near the home's foundation. After the site has been dry for several weeks, the springtails should move on. Whatever product the company is spraying with isn't working, so don't waste your time and money on that again. Springtails are rarely a problem inside homes, so I can't recommend chemical insecticides.