Read your Guidelines!!!!!!!!
The guidelines for the Dim Weight shop specify that the weight of the box must be between 2.5 and 3.5 pounds. There are also other restrictions related to timing of the shops. Don't rely on what you read here, I've seen it be wrong too many times, your guideline is the bible.
Now that I have that out of the way.....
The shops are not difficult at all but you need to be organized and listen intently or get a cheap voice recorder to record the shop itself, which depending on the line can take as little as 5 minutes. The recorder is highly suggested, as it will not only record what is said during the transaction (and in what order, which is important) but will also do your timings for you (start the recording with the exact time, including seconds....then say WALKING IN when you walk in, LINE when you come to a stop at the line, etc. then when ready to report just listen and note the times) and right after you walk out of the place (or even during if you do it under your breath) you can say how many in line, who was in front of you, etc. etc. and have all that info recorded for when you're ready to input.
My SOP now is to go to Walmart, get some boxes (guidelines for correct sizes, and for B you get the box in the actual shipping place), get some cans of different sizes and head to the produce scales. Weigh up the box and cans then choose the mix that fits the weight requirements of the scenario you're performing, all while ignoring the funny looks. :-) I put the stuff in the box and tape it down so it doesn't roll around and cause interesting conversations when I ask for insurance. :-)