If you dont want the hassle of bargaining, you should use the words "firm" and "serious buyers only"
I was trying to sell my sofa set as I had got another one on OLX but the guy was irritating me to reduce from 10K to 7K. I told him 8K was my final. He walked away and was still calling me. So told him I will donate but not sell it to him...
I've had good experiences buying on OLX though. Just got a TT table for my kids and before that a TT bat from Baroda, shipped to Chennai. Also got a nice sofa set. Selling has been a bit of a bother.