Some hobby shops probably don't know anymore about engine problems than you do even though they won't admit it. I'd tell them to either replace it, refund your money or you're never shoping there again. I'll bet the carburator is so out of adjustment you'll need a super tigre specialist to get it running. Someone that knows what they are doing.

Once you get a super tigre engine adjusted properly they run almost as good as any other, especially for the price!