Constant distractions from customers often interfere with work in the office.
The word that should be best used to fill up the blank is "interfere." An interference is a disruption of a work in progress.
So, when it is said that customers often interfere with work in the office, it means that they sometimes disrupt the smooth flow of office work.
Learn more about customer distractions here:
https://brainly.com/question/24898245