I seriously think your first mistake is not to indicate how much you are looking for.
BT-4's can vary in price (some can go from $65 and as high as $600, if not more) depending of the additional items and mods to the marker. On top of that, you have a custom paint job: Was it done professionally? This is also really hard to make an offer without this info.
People are also weary of offering without having a broad ballpark of how much the seller is looking for.
IMHO, way too many sellers get their "knickers in a knot" when offered a low ball bid...
Good luck selling