The only problem I've encountered was due to age or aluminum. Stare Farm insures my Mom's house and has given her a time limit to upgrade from the 1950's 2-wire fused system she's got or they will raise the rates but they will not drop her. I've heard similar stories from others. If you can pay the premium you can insure almost anything- but that may mean going to a spe******t and not your usual agents.
I too think the best thing to do is ask your current agent if the coverage is transferable to a new owner or if they will issue a new policy to them. They don't want to say no to an existing customer who probably has other policies with them and is likely going to insure their new home with them too when they move out, but they might say no to someone who isn't doing business with them already such as your prospective buyer.