not a non-stop flight out of China

I have a confirmed ticket out of Beijing to Tokyo, but with a several hour layover in Guangzhou. does this connection disqualify me from the visa exemption if I were to arrive from US to Beijing within the 144 hours?
If I am not eligible, will I be denied boarding before even flying to China? or what would happen when I land and am denied the free transit exemption?

also, would I be allowed to fly into Shanghai for a few days and then take a train to Beijing for a few days and fly out of Beijing to Japan if it were within the 144 hours?

Thank you for your help.