Writing a letter sounds like a very good idea.
It is very frustrating, indeed, when you find an overbearing salesperson or clerk. Recently I was looking for a backing for a baby quilt. The store was huge and I was shopping on holiday with my mother, father, daughter, and 1 year old grandson. It was a special coupon day and really a challenge to keep track of everyone. There were long lines at the cutting station and checkout. We were on a tight schedule.
At the cutting station, I laid out the fabric and quilt--measuring the amount of fabric I wished to order. The fabric was not that expensive, in my opinion, and there was a huge bolt of it. However, the cutter insisted that the quantity I wished to purchase would be "overkill" for the project. She was adamant that I buy a much lesser quantity. Unfortunately I listened to her advice. Later my mother said the fabric shrank quite a bit and would need to go width-wise on the quilt rather than length wise. It was a disappointment for us, but I've learned from the experience.
I like online fabric shopping. My name is Gerry and I'm a fabricoholic . . . I just remembered that Fabric Depot allows purchases of fabric in other than 1/2 yard increments. Off to take a look.