You may be right. But there is something more important than the grind that very few people will tell you about.
Water.
I suspect the store has RO water (reverse osmosis)+(possibly with remineralisation).
RO + Remineralisation is not easy, cheap or conducive for most homes. There are a few ways around this:
a. Always start with water from the cold water tap. Lets it run for 10-30 seconds if possible.
b. Use a thermometer if you're not already using one. You should find your ideal temp. in the 195-205F range.
c. You could use bottled water. Not as cheap as tap water, way cheaper than RO.
d. Invest in a decent grinder. It does not have to be expensive. If you don't mind some hard work, look into the Hario Skerton or Hario Mini Mill. In the lower range you could find something like a Breville or a Baratza Encore. If you absolutely must you could get a Cuisinart Burr Mill (Should be about $40).
e. Since you mentioned that you often buy coffee on the same day as it was roasted. Most coffee's don't taste spectacular on the day they were roasted and need 1-7 days to de-gas. When you buy it that fresh, move it to a glass jar and leave the lid slightly open for 5-12 hours. After the close the lid. Attempt at not consuming the coffee for 1 - 2 days.
Regardless how long ago the coffee was roasted keep it in a glass jar and air tight. Oxygen and air in general kills coffee. Quick.
It has the strange and useful behavior of spraying the fine particles (the "dust") against the top of the cup, where the stick, whereas the larger, correctly-sized particles fall to the bottom. After I grind, I carefully slide my finger to remove the dust from the top/side of the cup before pouring the grounds into my brew device.
Less dust = less over-extraction = less bitter.
I wish there were a sub-$100 burr grinder that doesn't suck... but alas.
There are, they just require a little elbow greece ;) In particular, the Porlex pointed out above has dropped in price quite a bit (I bought mine for $80 on amazon a year ago - now it's only $40).
Water.
I suspect the store has RO water (reverse osmosis)+(possibly with remineralisation).
RO + Remineralisation is not easy, cheap or conducive for most homes. There are a few ways around this:
a. Always start with water from the cold water tap. Lets it run for 10-30 seconds if possible.
b. Use a thermometer if you're not already using one. You should find your ideal temp. in the 195-205F range.
c. You could use bottled water. Not as cheap as tap water, way cheaper than RO.
d. Invest in a decent grinder. It does not have to be expensive. If you don't mind some hard work, look into the Hario Skerton or Hario Mini Mill. In the lower range you could find something like a Breville or a Baratza Encore. If you absolutely must you could get a Cuisinart Burr Mill (Should be about $40).
e. Since you mentioned that you often buy coffee on the same day as it was roasted. Most coffee's don't taste spectacular on the day they were roasted and need 1-7 days to de-gas. When you buy it that fresh, move it to a glass jar and leave the lid slightly open for 5-12 hours. After the close the lid. Attempt at not consuming the coffee for 1 - 2 days.
Regardless how long ago the coffee was roasted keep it in a glass jar and air tight. Oxygen and air in general kills coffee. Quick.
f. Grind 30 seconds before brewing.