Door to Door vacuum cleaner salesmen. It feels dirty just typing it.
Dodgy as business I worked at when I got out of school, they would actively encourage you to rip off and manipulate pensioners. They're entire sales tactic was illegal and based on lying. As soon as you got in the door it was encouraged to not leave until you had a sale and the police had to be called on a few ocassions because the people just wouldn't leave.
Worst part was the vacuum cleaner itself was sold at ~$5500, with around $4500 wiggle room to get a sale. I had loose morals at that age but even it was too dodgy for me.