Is it an Optimist?
Real Optimists carry a little blue numbered label called a "BUILDING FEE PLAQUE" like the below (it adds just US$50 to the price).
Subject to measurement (carried out at time of manufacture in the case of GRP boats) this label means that this boat is built according to the rules of the Optimist class and World Sailing. It can take part in Optimist races anywhere, from the next bay to the other side of the world . . . . and always will be able to.
The success of the Optimist has led several big companies to produce cheap copies knowing that they don't conform to Class Rules. These are frequently passed off as Optimists, usually amid the bright lights of boat shows by unscrupulous dealers.
IMITATION BOATS ARE NOT ALLOWED TO RACE WITH OPTIMISTS.
You may also find that they are as difficult to re-sell as that "Rolex" you bought on holiday for $10 from a street-vendor. Genuine Optimists start around US$2,000 new, much less second-hand. It's worth paying the difference.
Contact your nearest builder or National Optimist Association for further details.