Car Dollies Needed....Make or Buy??

I never had any issues moving my cars around my shop by myself on the dollies, complete cars included. On a sloped driveway I needed two people.

But this shouldn't be surprising, how easy do you think it's going to be to move a 3,500 lb car? They're just dollies, they don't defeat the laws of physics.
I wonder if they had a bad run of casters? I have an OLD floor jack I got from them when they first opened in Macon YEARS ago. The jack works GREAT but it rolls like crap. I need to get up off my butt and put some better casters on it. I have a better jack I use on the concrete floor, but I use the old one outside so it's not a huge deal.