Honestly, since you’re the buyer, there’s no real reason not to use a realtor (because they’ll take their money from the seller, not you). I’d just be sure to get one who knows their stuff (i.e. – make sure they have some level of experience dealing with vacant land, as it’s a whole different animal than what most realtors are used to dealing with).
If your property and those around it have recently been rezoned, this could be a sign you can sell your property to a developer for a good profit. But nothing is set in stone. The next best step is to speak to your real estate agent, who will know what has recently sold and whether any developers are actively looking in your area. They can then assess your home to see whether it would be able to sell and some estimated figures.
Market for Land is Less Active – The market for existing homes is almost always more vibrant than the land market. There simply are fewer numbers of buyers for vacant land than consumers looking for homes. Start marketing a new home listing and a new lot listing when both are desirable and priced well, and you generally can expect fewer contacts about the new lot listing.