I've only brewed from a kit once, and it was bought for someone else and brewed with someone else (brother in law's first batch). Other than that, I assemble on my own. Like Yooper, I buy in bulk. I have a few ingredients I tend to keep on hand (Maris Otter malt and German pilsner malt, both bought by the sack), I keep a stock of East Kent Goldings in the freezer (bought by the pound), and then I usually keep a few pounds on hand of various specialty malts (45L, 77L, and 150L English crystal malts, Biscuit malt, and Carapils), as well as maybe a half pound of Challenger hops (which I could order online by the pound but my LHBS only stocks by the ounce). And then I usually have some 1469 West Yorkshire on hand, either via smack pack or harvested slurry. Beyond that, I buy other grains/hops/yeast as I need them. Also keep ready stocks of corn sugar for priming, DME for starters, and all the other misc stuff (Star-San, whirfloc, yeast nutrient, water additives, campden tabs, PBW, pH meter calibration solutions, and so on).
There's nothing inherently wrong with kits, and at the end of the day there's no inherent difference betwee brewing a kit or brewing someone else's recipe outside of the actual ingredients being assembled already, but unless the store has super high turnaround I'd be worried about the freshness of the ingredients. I'd be fine buying a kit from Northern Brewer or the like, but I'd be cautious buying one from a local shop unless you know them really well. If you assemble the ingredients yourself, with yeast and hops that have been stored properly instead of in a box at room temp, with grains that were crushed right before you use them instead of sitting crushed for god only knows how many months, you're going to get better results.
