I bet it depends on area, but I've never seen any reputable dressage trainer to post on Craigslist in my area. They pay for the ad in Equiery or go by recommendations (and some don't even take any new students in). And yes, to me the ad sounds strange.
If you like the place I'd watch several lessons of different levels before making your decision.
"Life isn't about waiting for the storm to pass: it's about learning to dance in the rain..."
"When we are no longer able to change a situation - we are challenged to change ourselves."
"How people treat you is their karma; how you react is yours."