The effect of yeast on beer flavors

[Yooper]

When I was at my lhbs the guy mentioned that he thought new homebrewers chronically underpitched. I asked if you could over pitch and he said yes but it's hard. Thoughts?

It's very difficult to overpitch! Not impossible, but difficult for sure.

Check out yeastcalc.com or mrmalty.com and look at recommended pitching rates for yeast.

One vial or smackpack is underpitching in almost all cases, and starters are recommended for any 5 gallon batch over about 1.040.