Selling parts and lack of manners.

I have been on both sides of the fence

Lately as a seller i post up the ad and get a a lot of people asking for shipping quotes. I usually take the first one and give him a quote. Then sit, however i have had many people that never reply back as to which way they will go with the item. Lately if i remember i try to get a read receipt when i send a quote. As soon as i see it has been read i give them a day and i move to the next and send a quote to next in line and keep progressing down the line.
This method gets very frustrating, but i feel its the best method. I look at every pm as a tire kicker and do not take them seriously until i have the cash in my hand.
I have also been burned by people that say they will take an item and then never pay or never hear back from them while the part sits on the shelf ready to go out while i use my courtesy.
I was very frustrated a few weeks back and when I got caught up with all the shipping of stuff and pms. I had to take a break from even replying or logging into the site because i was so frustrated with all the tire kicking and doing quotes. I try to ship the cheapest way possible so i always try to tuck a bunch of parts together when possible so nothing is boxed up until i make up a quote hoping to save the buyer money.
Most of the parts i have up for sale is money i need to get the last items for my car, but the last few months it was about rent money and groceries. So this is where cash has been talking more then waiting around.
I have also found that selling parts can get very stressful at times when you have a lot of parts listed at the same time.