Can I put deals under contract with a listing agent? And if so is the listing agent required to take the listing down?
Yes but wholesaling something that is on market is incredibly difficult because every investor worth their salt has already seen it and passed on it.
You're much better off having a good source of buyers. If you have a good deal, contact them directly. Someone will want it, and the more buyers who see it, the more likely you'll get an even better deal!
A smart agent is going to protect the seller and not fall for unlicensed broker tricks.