The easiest thing to do when buying a domain is to trust a seller with what they post for information on the selling page but the fact is you really need to do your own research. Check things that matter to you the most and you really do not have to follow what the seller posts at all!
The number one thing to do is a search on Google of the domain with the extension at the end. You can find out a lot of info on a domain that way. If the domain happened to be sold recently, you might find out what they paid for it! If the domain was stolen, you might find a posting on a forum etc.
If you are buying directly from a seller, get as much info as you can. If you request a phone call and they deny, you might want to think again. It’s always best to buy from somebody who is very open.
Trademarks is often something many people just assume there isn’t one. So going to uspto.gov and doing a quick and free keyword search can save you a headache down the road.
Check to see if the domain name is indexed with search engines. It can takes Months to get indexed, so if it’s indexed for a keyword you are interested in already, all the better. You might even be smarter then the seller and they might not of even done this, which does raise the value of the domain. RankingCheck.com is a nice free tool or just type site:domainname.com into your search engine.
Compare other sales of domain names matching keywords or the pattern of your domain if it’s a 2 letter/character, 3 letter/character etc via NameBio.com .
You can also use Whois.sc to check and see if the domain is Blacklisted (used for spam), how many other extensions are registered and if they are parked or web sites, creation date, expire date, registrar etc.
Depending on what information is important to you, is where you should check next. Advertising value of the keyword, how many people search for your domain term per month and so on. Just keep in mind that the seller is trying to Sell, so the info provided might not be 100% correct or they might leave a little info out as well. You can always email me if you have any questions, as I am always willing to help.


Nice article
Google trend is also a good tool to see if the keyword is worth to buy.
https://adwords.google.com/select/TrafficEstimatorSandbox and https://adwords.google.it/select/KeywordToolExternal are two useful tools to see if there are a lot of competition for the keyword and what is the PPC
June 17th, 2008