I am pretty good about updating my adds as well and those that don't annoy the heck out of me as well.
It is too bad that some people ruin a good thing for others. On CL, it is pretty much the wild west. There are robo adds that keep popping up every few days. Then, what really ticks me off is those that put a ton of key words in their adds that trigger search hits that typically have nothing to do with the search terms. There is a guy that parts out vehicles supposedly and every day a new vehicle gets highlighted but he has every make and model of vehicle in the adds along with every auto part name that you could think of so any time someone searches for "Mustang", his add is sure to show up even though it is a KIA Serento parts listing.
There is also another guy on my local CL (probably on a lot of area CL's) that posts higher end items like cars or ATV's for prices that are really good, but not so good that you immediately dismiss them. I am sure they are just doing some kind of Email address collection or something. They usually pop up several times over a week or so and then go away for a while.
Then, FB MP has its faults too. First, I hate that it doesn't seem to list search results in any logical order. It doesn't seem like the search results are in chronological order for sure and it doesn't let you know exactly how long the listing has been up. Also, it does mark listings that you already looked at as "Read" or anything. It is just confusing and I have missed several good rehab candidates because of it. I also don't know what the problem is, but if you search for "WEBER" it seems like you might as well just search for "GRILL" because you get every make and style of grill on FB MP.
But, Hey it's free so I won't complain too much. Offer Up and Leto around here are useless.