I put myself in the eyes of the customer. ....I go in there and feel like I "am" the customer and how that customer would respond to being ignored, or, on the other hand, being totally taken care of by a conscientious associate.
The other part of me is who I am and why I am really there: To report back to the client, an honest assessment of what happened during the shop.
Do I feel bad about taking 20 minutes of the associates time? No. Is this person making commission on sales? Is his only compensation commission on the phone sale or is he hourly/salaried?
If he was commission only, then yes, it would bother me that I was taking food out of his mouth because I have no intention of purchasing anything from him. To my knowledge, they are not commission only. (I hope) but then, I don't do that many cell phone shops (maybe 8-10 a month, if that)