How can I tell if my Pok�mon Leaf Green is hacked?

For christmas I got the 5 third gen pokemon games and I started playing leaf green. What makes me think it's hacked is that I've come across 2 shiny pokemon, one shiny haunter which I caught, and a shiny Dratini in safari zone which got away. With only 75 hours of playing time and the odds of finding a shiny being about 1 in 8200, I think my game may have been hacked; I bought it used and it was shipped from Hong Kong (sounds shady right?). There are no other noticeable problems with the game, my pokemon stats all seem normal etc. I don't mind the extra shinies, I'd just like to know if there is a way to tell if it's been hacked.