Bike Shop rip off or reality?

I needed a few smaller items that I couldn't just run into The Hub to get because I'm about 700 miles away from Webster Groves! Anyhow I forgot to ship an air pump out here so I purchased a $20 one from this local shop. I also purchased several GU's and power bars. Today, I was looking for a small part and this shop did have what I needed and the shop worker asked if I wanted them to install it. I was still in my work clothes and had my bike in the trunk of rental and thought well sure this will save me sometime so I don't have to do it when I get to hotel. Only one problem, they wanted $10 to do it. I intentionally didn't say what the part was, so I could reveal that now. I bought a Cateye computer. So after spending $60 on this, you want $10 more to install it, I don't think so. It's already marked up for profit and you still want more!??!!? Do shops really charge that type of fee to install a wireless computer? Needless to say I was pretty turned off by that.