Hi Bonnie,
I invest in multi families in the Brattleboro area and I would not consider a property listed at $227K with total potential rents of $2200/month. I don't know any investor that would consider that deal. especially considering the high property taxes in vermont, investments for me need to be close to the 2% rule, meaning monthly rents would need to be 2% of the purchase price. in the case of a property listed at $227K I would be looking for rents of $4500/month.
you mention single families selling for more than your duplex, this is because the buyers are completely different people. Someone looking at a single family is buying on emotion and will pay more to get a house they really want to live in. Someone buying a duplex is buying for the investment, the property doesn't need to appeal to them emotionally it just needs to make since financially, your property doesn't seem to make financial since for an investor. You could end up selling to someone that really likes the property and likes the idea of having an extra unit to help defray mortgage costs, but that would be a very specific kind of buyer as most people just looking to buy a house don't want to be a landlord. Is there any chance you could convert the property into a single family? That could actually increase its value.