That would depend on a lot of things. If it’s a really good fake (that’s about 15% of the fakes out there), there is no difference between the fake and the original. The pj is the same, the frame is the same, etc, etc, etc. The only way to tell is if the racquet has a serial number (ex. on the plastic covering for the grip) and call up the racquet company.
For the not-so-great fakes, there are different things to look for. If you’re buying a racquet online, good luck. Most companies will post pics of the real thing and send out fakes. If you can actually touch the racquet (or see it), check out the pj. Most fakes’ pj’s are slightly different in color than the real ones. Also, if it’s a babolat, check to see if there are woofer grommets. Also, see if the weight is about right. Chances are, you’re not going to have a very accurate scale on you, but if the racquet is supposed to be 12 ounces and the fake is really light… Also, most fakes don’t get the hh-hl thing right. I’ve seen fake PDR that were around 7-8 points hh.
Hope this helps.
Fake Babolat from Tennis Rackets for less. There were spelling mistakes on the card insert, the finish on the handle was rough and the BABOLAT name on the inside of the racket was not solid print. Stringing strap around outer edge of racket was broken. The racket came unstrung and cost $99 so it was not exactly cheap, stringing would have brought it close to most other prices. Fact is if it is coming from China it probably is fake. Having said that I paid thru PayPal and the seller has agreed to a full refund including shipping if I return the racket.