Thankfully I never had to lift anything too bulky working in a grocery store but there were boxes up to 70lbs.
Ordinarily I could lift them but while pregnant I was restricted to lifting 25lbs; doctors orders and my awesome manager would have had a fit if she'd seen me trying to life more.
I only had one customer pitch a fit at me about it surprisingly enough. She asked for a case of a product which weighed about 35, maybe 40lbs. I had to tell her I'd go grab someone else to lift it for her and she started bitching. I briefly explained that I wasn't able to lift more then 25lbs and she started in on the, "You shouldn't be working here if you can't do your job," crap.
I briefly considered shoving her in the compactor but instead I just said, "I'll just go find someone who isn't pregnant to lift that for you."
Yeah, she apologized after that little guilt trip :-)