We have a 2017 Greyhawk 29W which we bought new and really like. Did have a number of minor problems that I was able to fix myself. Hopefully your previous owner worked out the old kinks.
From what I have read on this forum, Jayco started to cheapen things in 2018. Apparently the counter tops and back splashes are much cheaper in construction. Maybe other things as well.
I would say a 2017 would probably be a good buy if it is in good shape. Make sure to test all items such as generator, AC, slides, inverter, etc.
Lastly, there is a current recall for the leveler mounting bracket. You may want to ask if they have done anything to strengthen the mount bracket. Not a major deal breaker. You just don't want the surprise of the pump falling off while driving. There are multiple posts in this forum regarding this recall.
Retired electronic technician (45 years in the field)
2017 Greyhawk 29W
solar & many other mods
wife (maybe I should have given her top billing)