I have Bought many Bikes Quads & Minimotos from eBay Sellers, I use them then sell them on, I find all the Chinese Bikes Minimotos & Quads have the same problem it may be a CG replica or a Trials Bike Copy Or Suzuki Copy Quad, The First thing to go wrong are like other eBay users have noticed the fuel lines leak or the fuel tap, I replace this with a genuine one from a motorbike spares shop, The fuel Filters normaly leak or are cracked, I by pass these & take the filter out the bike runs ok without them just put a new bit of fuel pipe in, run it from the carb to the tank, you can buy the pipe from a car spares shop by the metre. about 40p a length. The other things that go wrong are the Battery won't start the engine you can't even kick start them, You can buy a good bike battery at Halfords or a car parts shop normaly the same size for about £20.00 this normaly does the trick they are Jap batterys & are of good quality, Other things the bike rattles its self to bits, I have had them where bits go missing on the road or your reg plate falls off, what I do now is put lock tight glue on all them nuts & bolts that hold the plastics & all them parts together also once a week go over them with a spanner or screwdriver & tighten them up just incase they working them self loose, also use rubber insulation as a anti vibration pad it stops the parts cracking or spliting some times. The last thing is always change the oil in them for some good quality 4 stroke oil  you can get 4 LTRS of oil for about £5,00 & its better than the import oil in them also if you can get a replacement Spark plug do it, as the ones that are in are not very reliable. I hope these tips help!, I have had these types of bikes since they hit the UK market & they are fine Cheap & Cheerful, EUROPA TRADERS, YOUNGS INTERNATIONAL, LLEXETER, have supplied most to me (EUROPA HAVE NOW STOPPED TRADING ON EBAY) & I have found there items GREAT VALUE for MONEY, I have done 5,000 Mls plus on a 125cc Custom copy from them & it still runs fine, BUT  ALWAYS REMEBER THIS YOU CAN'T BEAT THE REAL THING FOR BUILD QUALITY, RELIABILITY & MOST OF ALL SAFETY.