A few years ago we raised our prices substantially and that reduced to near zero the number of nasty pre-sales support requests (we have a demo for download). S

A few years ago we raised our prices substantially and that reduced to near zero the number of nasty pre-sales support requests (we have a demo for download). So yes, higher paying customers are generally nicer. We also had a case similar to the OP where some guy kept emailing us for months because we didn't solve some problem he had even though it wasn't directly related to our product.