A Domain Registrar is a body which has been authorised to sell top-level domains. Companies like Register.com and NetworkSOlutions.com have been authorised to sell and sub-contract selling of domains. Since they are the primary domain name sellers, they usually charge highest. Since they ar ebased in the US, the comfort factor for buyers in India is less.
Domain ame resellers in India like Direct Information, Net4Domains sell domains for far cheaper - less than Rs 600 for a 1 year validity.
Apart from cheaper costs, the other factor to look out for is a good user interface. A user interface is useful for the buyer to be able to change the contact addresses, primary and secondary name servers details, (the web servers where the website is hosted), renewing the web domain, etc.
Therefore, if the price is cheap and the company provides a good user interface on its website, and if the staff of the company is friendly and helpful, the buyer should have no reason to hesitate to buy a web domain.
Do remember than all domains ending with .in are registered solely with NCST(https://domain.ncst.ernet.in)