if bike isnt performing and doesnt feel right, your probably best to go and get it serviced, if you dont know what your doing and to be sure. safety first.
paying some to work on your china? BLASPHEMY!!
when your bike's only worth a few hundred bucks what's the point of paying someone to do stuff you can easily do yourself? these bikes need servicing after every 3-4 rides and some things after every ride, you'll be paying twice what the bike's worth in no time.
this site has all the info you need to learn how to take care of your bike and these bikes are really easy to work on