Explain what "flat" actually means in your cup right now. Is it just missing the fruity punch the $18 bag had, or does it taste weak and watery like you underdosed? Because those are two totally different problems. If the cheap stuff just tastes boring but still has body, you can fix that with a slightly finer grind or a touch more coffee per cup. But if it's thin and sad no matter what you do, that's the roast, not you.

That Spokane shop detail got me. I used to be the guy who just replaced the whole board without even looking at the old one, figured a $2 cap swap was just something old radio guys did to feel smart. Then I fixed a 2004 treadmill that way, a $3 cap on the motor control board, and it still runs. Now I pull the board and look for a bulging top before I spend anything. It's saved me a few hundred bucks and a lot of trash.