IMy local super market may end up losing a trolley as well to put my scope etc on..... but i never said that.
Make sure that the wheels are in good condition, and when you modify it add a small length of chain
( if not present already) on the back non turning wheel so that 2 links can dangle on the ground to avoid static build up.
Depending on the trolley ( 2 basket only or the larger type with a steel mesh basket) you might want to make a top wooden cover, and cut a hole in the mesh for access when it is on.
Small trolleys you want to make the basket frame level, most are sloped and things will slide off.
No, I bought the trolleys I modified, from the local shelving supplier.........
I did make some trolleys for work, but they complained about the cost. They have outlasted the cheap ones though, those cheapies all were scrapped after breaking. The ones I made from angle iron, and which were hot dip galvanised, are all still in daily use.