If we assume that's true, it would imply marketing works, would it not?

It implies that marketing works for marketing. It's possible that those involved in the marketing sector are more vulnerable to marketing. This vulnerability could be the reason that they have faith in the sector's methods, and are therefore employed in the sector.

Many people are marketing averse, and marketing at them will have a negative effect. It just seems that there are enough people around who respond positively to marketing to make it a successful business.