Hmm, just sounds like a case of beans unfresh beans. You definitely should be able to get a good shot out of that machine. I used a San Marino a while back now and with fresh beans I was able to get good shots with crema that tasted good.
What type of routine are you using, dosage, tamp etc.
Has the machine been regularly serviced, ie, a good backflush, descale etc, etc
What recommendations did the bean rep give?