These are not brand new rackets, but are in the best of conditions and can be easily passed on as new products. Many of the well known brands sell these types of rockets and many people; in fact, have had a great experience buying these used ones.
Used tennis rackets imply that these products have been played with. They are generally shipped in their current condition, including strings and grip and no cover unless noted in the racket detail description. If you want these used tennis rackets to be re-strung, then you have to specify that. When such clothing accessories and tennis bags are purchased, the policy is to immediately reimburse the selling customer with store credit. The descriptions & expectations of unseen used equipment can differ. The person selling is responsible for setting the selling price and gets store credit after the sale is complete.
Usually, companies scrutinize these used tennis rackets well for any damage and deformation before making them available for sale. These products are usually in the perfect conditions and have been used, but very few times. If they do not meet the customer standards, they can send them back, to be re-sold.
Thus, if you want to buy a used racket, you can go to any well known and famed tennis racket store and get it from them or order online. In case of any problems they will change the rackets as per their policy. They can be used by all and they respond well as they have already been tested and played with. So, no need to fear while buying used rackets, as they are often in the best of conditions and companies would not sell these if they were not fit for selling. So, don’t be tensed and get your racket as soon as possible.