I think you might be going about this the wrong way mate,
i just sold my car a couple of weeks ago, the car sold within 4 days of being advertised... I recieved both emails and also phone calls for the car
for someone to actually pick up the phone and call me shows they actually have some serious intent, but an e-mail just doesn't really cut it with me when it comes to communication, so when you say, you think some people arent interested in selling because they don't reply to your emails, perhaps you should try ringing them instead
needless to say I sold my car to someone who rang me, he came when he said he would (on the phone) to inspect it and he bought it