Is it a bad idea to buy a used gas bottle?

[Marko6556]

I've used CO2 pub gas since I started Mig welding three years ago. Just tried a disposable C14 mix for the first time today. Yes, it's nicer to weld with, but not massively so. I've tried it on 2mm lap weld and 4mm fillet so far, I will try on some 1mm and 0.8mm tomorrow.
Argon mix is very expensive where I live, in Portugal, but my local bar charges me €50 deposit, returnable, any €48 for the first bottle of gas. No problem swapping for new bottles.
Perhaps because I learned to mig with CO2 , so I'm very used to it. I find it fine to weld with. Previously welded with stick.

 

[Nomad]

I've been using co2 since is stated with mig 20+ years ago, using a mix of pub bottles & fire extinguishers.

Fire extinguishers used to work well with repeated on & off use, newer ones seem to be designed for single use so the seal starts to leak gas after a few uses.

No problem getting pub co2 bottles refilled at my local fire extinguisher shop (proper old school, newer by-the-book places might have different systems).

Most of my work is car bodywork and I find co2 gives good results even on butt flush joints.

Don't rule out co2