It seems incredibly helpful to perform a general calibration and tuning of the printer, for which there are a number of guides. This can often rectify the problem, and also produces example good quality prints so that the problem can be further narrowed in on.
My personal experience was of stringiness on one printer. I thoroughly cleaned and purged the print head, tuned the temperature, etc; it ended up turning out the wrong size nozzle was on for the print. It can be a number of things.
