That could be a good idea. Imagine you put your player for sale on a thursday w/ a transfer add, and then on friday he pops. Then you might wish you said something else, like "Look at the little green arrow!!!!!!!!" (kidding)
Concerning the usefulness of the ads, my opinion is that they help. As long as you don't make them too long, and keep it real. Players that are not outstanding are more common in the market, so the ad gives a little more visibility. And if more people see your player, you're likely to have more bidders, and that can be the difference between selling someone for 250k or for 300k.
As for someone who asked if you can see your ads, try refreshing the player market page a few times close to the sale deadline. Sometimes my ads show up then.