Olx.in is one of the largest and most frequented web portal for selling and buying used stuffs. You can sell and buy almost any thing, starting from a read book to a used 2-wheeler or 4-wheeler and much more.
However there are some limitations also which you have to consider while making a transaction on OLX, especially when you are buying something. What seller purports to be may not always be true and you have to be wary of that. Personally, I bought a book from OLX few days back. And after purchase.
I found that the book was a much older edition than as described by the seller. Additionally, some pages from in between were missing from the book about which the seller had written nothing. OLX needs to create some guidelines about selling things for seller, only then it can win the trust of buyers.