Advice on where to get quality rods/shafts for my printer?

I am from the US.

I wanted to replace the smooth rods my printer came with as it was a fairly cheap model and I am worried all of my assembly/disassembly from tweaking and upgrading it could have bent them. Plus, I just wanted higher-specced rods than the cheap ones it came with.

I tried buying them from someone others insisted sold high quality rods on eBay, a US seller, however when I got them they don't seem to work right. Despite my calipers (which I admit aren't high-end) reporting them as both being the same diameter, both my old and new sets of bearings don't work smoothly on them at all, while they work fine on my old rods.

After this, I had many people joke to me about parts made out of "Chinesium" and how they tend to have to order multiple parts to get a working set. After this, I am done with eBay, random 3rd parties on Amazon, AliExpress, etc. I wanted people's opinions on what are actual reliable sellers of good quality rods I can use for my printer. Issue is, I have very little experience with industrial terminology and ordering industrial parts. I tried ordering looking for the rods at McMaster Carr, but the lowest I was able to drill down was to three options ("Corrosion-Resistant Rotary Shafts", "Linear Motion Shafts", and "Corrosion-Resistant Linear Motion Shafts") of which I couldn't tell the difference between and they only seemed to come in specific lengths. I don't have the tools nor the expertise to cut them to length myself.

Can anyone offer any advice on where are some places I can get actual reliable rods for my printer, and what I should be looking for when I order?