It is to good to be true, for most sites, but there are some good catches out there.
Man dude just a check list you have to go through when you purchasing a site.
* The first thing you need to remember is that you should try to buy website with minimum amount of work required. That is the key to building your "online real-estate empire".
* Always use escrow service. Even if it is at the cost of your own money. This will give you time to verify ALL the claims by the seller about the monthly traffic and revenue. If those claims are not met, feel free to reject the deal.
* When viewing the traffic stats, make sure you view the referrals stats as well. These days many people create quick traffic with sites like digg and stumbleupon and then sell the website. Such websites may not have a good business model to work on in the long run. So make sure that you view the referral stats to see how much traffic is coming from search engines. If around 70%+ traffic is coming from various search engines, you are good to go.
* If the seller is not using adsense on his website, make sure he is not banned from using it.
* When person is showing the revenue stats (lets say from adsense), make sure that CTR is not very high. If it is too high, make sure that the
person is not in any sort of violation of policy on the page, for example, images above the ads, extra attention to the ads, etc.
* When you see the page rank of the website, don't just believe it. Check the back-links of the website and verify that these back-links actually make sense with respect to the page rank of the site.
* When verifying the back-links, check if there are many site-wide back-links. If yes, ask the person whether these are his own sites. If yes, ask him how long the the links will stay. If not, ask him what sort of understanding with the other site is, so that those links can stay there.
* Make sure that internal pages of the site also have some page rank.
* Ask the seller if he has ever sold any site before (on the same forum/marketplace or other). If yes, check his history and transaction with previous buyers.
* Make sure that the site is listed in Google and pages are cached.
* Make sure you ask the seller whether the content on the site is unique. If yes, ask him who has written the content. Use the copyscape to verify what the person says. Also inquire about the images used on the website. Make sure they are not in any copyright violation with some other site. If they are, you should know about it.
* Check the age of the site. The older the better. Check the archive of the website at archive.org to see what has been the past of the site. Make sure it is not a site which was created on a old domain grabbed which had some other site in past.
* Ask the person whether he bought the site from somebody else. If yes, when.
* Find out what softwares/scripts he is using on the site. Make sure you are comfortable with those. Else it can create problem later on.
* Don't ever belive the "webalizer" stats. They are much inflated. Ask the person to provide stats from any third party like google analytics or scripts like awstats.
* Last and finally, ask the person if he/she would help you moving the site to your server. Most people will agree to it, but its always good to ask first.
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Sitepoint and DP are the best place to look for deals.
I bought a site for $500, that was making $5/day, that is only like 4 month rev, I bought it a month ago, and it is not making $9/day, about $270/month, and it has made me in total $212.52 in adsense, already nearly half way there in a month.
It is definitely possible, and I have never bought a site that has flopped.
Never buy sites that are making big monthly income, buy multiple sites making small income ie, 10 sites making $300/month,$10/day, = $3'000/month, is the more intelligent may to go about it.
Make sure to see that the user is trusted etc, in DP and in sitepoints. Look at other sales etc.