I mean, that's a bet I'll take. Everyone exaggerates a bit, but there's no way you really believe 99 out of 100 marketing companies are making up fake coworkers and flat-out lying about their entire portfolio.
Probably a little exaggerated, make it 90%. Maybe top 1% is doing it right. Small / medium marketing companies are not telling the truth ever. Show me some marketing companies and I can spot their lies within minutes for you. I am very used to it.
You are exaggerating.. but not too far off. Having experience with small marketing agencies (which are very often actually just one dude), the amount of "creativity" in their "strategies" is insane, and probably criminal. And yes, they all claim everybody else is doing it too.