Yes, there are errors on PCBs from iTead from time to time (as there are with pcbs from all fabs). Most of the time the error is between 2 neighboring pads where the copper is not properly etched although it could also be between two traces or a trace and a pad or a pad and the gnd or power plane.
It's always a good idea to hold onto a couple PCBs in case this happens. I haven't personally had to deal with this (yet) but my plan is to refund and send a new pcb if (when) it happens as to help offset the cost for wasted components. Some mistakes are obvious, but I've seen some here on the forum that are very difficult to spot.
