Germany has an auction site for guns too. I can not think of the name. I am not into buying used guns. Sometimes you can get a great bargain. My friends use the site. Saved quite a bit of money with scopes and drilllings. Of course you need your WBK (weapons permit card) and a competition or hunting license. You need to also complete the weapons transfer paperwork. Easier with rifles, not as easy for handguns. Patience and crossing your ts and dotting your Is is the rule of the day (or months).
I have used gunbroker and buds gun shop. Both were trouble free experiences.
”The world is filled with violence. Because criminals carry guns, we decent law-abiding citizens should also have guns. Otherwise they will win and the decent people will lose.”
~James Earl Jones