Personally, here's what I'd write. Just my 2 cents. Additions are in green.
I have a been a customer at your GroceryStore for X years. Generally, I'm pleased with the service and happy to shop there. <== start on a good note, butter them up a bit, indicate that they've made $$ off you in the past and for a long time so they don't want to lose you as a customer
I am writing to express disappointment with the customer service at my local GroceryStore on a shopping trip tonight.
I went to GroceryStore at Location. I arrived there around 11:30 PM, and shopped for about an hour.
As I'm preparing for a holiday meal tomorrow, and bought a few last minute gifts, I had a full cart when I got to the checkout lanes at around 12:40 AM.
I looked for an open lane, but the only lanes open were the self checkout lanes. While I don't mind using the self checkouts if I have a smaller order, I really do not like using them as they frequently can't read things and I find them frustrating. I asked the employee who was overseeing the self checkouts,
a middle aged man named Mark, if someone could open a regular lane, since I had a full cart. His response was that there weren't any regular lanes open, and I would have to use the self checkout. I expressed concern that I wouldn't be able to fit all of my items in the small bagging area. To this, he responded, "Oh sure you can.. I do it all the time. You can take your bags off of the turnstile and put them over there." (pointing to the extra space, which is still small). He then turned around and walked back to his register.
Since I did not want to waste the hour I had spent shopping in your store, or go to another store and redo my shopping at that hour, I went ahead and started checking my groceries.
It ended up taking me about 10 minutes to get all of my groceries checked and bagged, and I did have to stack several bags and items on top of each other in the bagging area because there wasn't enough room.
At no time did Mark come back and offer to help, he stayed at the front of the checkouts talking to another employee.
I do realize that shopping late at night comes with some minor inconveniences such
as aisles being blocked by stock carts or littered with packing boxes, and some departments being closed. I do not expect poor customer service such as this, especially when I had asked for assistance in getting a lane open and was refused.
I would like to know if it is company policy that only self checkouts are available at certain times/hours. If it is, I would suggest that this be posted at the entrance of the store so that customers can make the decision whether to stay and shop. I would not have stayed, or at best I would have bought much less, if I had known I'd be checking my own groceries.
I spent $247.76 on this shopping trip, and had 72 items. I have to say that having to check out this order myself has not left me inclined to return to this store.