Yes it is for posting free but some parts I can require paid listing, premium member ship to access special areas..etc.
That's the problem that I am facing and finding best ways to have traffic for it.
I don't think you and I understand each other completely. You didn't answer my questions. Let me rephrase them and ask again.
You said that your website is a place that allows website sellers to post their website for sale. And you said that your website is a place where website buyers could come to find a website for sale. Right?
There are other websites that already do this. What I am asking you is
1) What benefit does a website seller have for listing their website for sale on your site instead of some other place or in addition to some other place?
and
2) What benefit does a website buyer have for coming to your website to look for a website to buy instead of going to other well known sites to look for a website to buy?
If your website doesn't offer a big enough benefit to those people, then you are probably not going to be able to generate substantial traffic to your site, at least not enough to make the site successful.
If you are sure that your website does offer a big benefit to those two groups of people, then you want to go figure out where those two groups of people are spending time online right now, and tell them about the benefits your site offers them. Here is one way you could do that. Go to a website like Flippa. Make a list of domain names that are for sale on that site right now. Use Whois to lookup who owns those domains. Send an email to those domain owners telling them that your site exists and telling them how they can benefit from using your site.
If you think that people are going to want to use your site just because your site exists, you will probably discover that you are wrong. A small number of people might try your site simply because they want to test it or because they might not know other sites exist that do what yours does. But, unless your site offers a real benefit, something better than they can get from another site in your niche that they already know about, then you are going to struggle to get any meaningful amount of traffic from anywhere.
If you build a site that is useful enough for a specific type of person, then it is simply a matter of finding out where that person is spending time online right now, (like which blogs, forums or Facebook groups they are visiting regularly). Then you go there and join those places and start talking to those people. Or else you buy advertising at those sites so that they discover your website for the first time.