I'd be pretty uncomfortable with a 6month closing date, unless it is a new build...(we need six months to build it) or there is some very unusual compelling circumstance which makes the buyer or seller want to wait this long.
I would want substantial earnest money from the buyer and perhaps even on a monthly basis, something like $1000 to start and $1000 on the 1st of every month to closing on a $200,000 sale. You could adjust up or down on other values.
Way way too many things can happen in six months. New jobs, new spouses, new kids, different credit requirements, deaths, accidents, tornadoes, and who knows what else. Think about this too....when do you do the inspection....Day 1....so how do you know things like AC units go bad between today and October?
Sales tax...that's a slippery slope to start down. 1% now....2%......next year....5%....5 years from now. With all the foreclosures and banks in bad shape, I don't think they'll let that happen.