Maybe it does get irritating, but that at the end of the day that is your problem. When buyers have options of BINs to choose from they are giving you the option to also provide it. You can choose to take it or not. They are not being rude, unreasonable and it sometimes works.

Just add in a high BIN option, if you are lucky and they need it enough you may get it.

Some buyers want to know for sure they can buy something and have it in the post ASAP, not wait for a week for a maybe win maybe not for who knows how much. Then start looking again.  for another if they loose.

If you want to succeed as a seller the aim is to provide a service buyers want not just just dictate what you feel like doing regardless of what the market wants.

Otherwise simply "no thanks" is enough response to questions like that, hardly a great effort in the scale of Ebay selling effort. A grumpy or reluctant response would leave me wondering as a buyer what your response would be to a real complaint or difficult question.