Sorry but when you have a great product at an already very fair price and you STILL get offers at 50% of your asking price (or less in a couple of instance) then it would try the patience of a saint.
And usually this has been accompanied by many irreverent emails even when you politely tell them their offer is not acceptable to but the product.
In general the whole attitude from buyers has changed considerably over the past 20 years with rudeness and brusque arrogance being all too common.