Bartering in Germany
 

Is it polite to barter with the vendors in the various outdoor markets you find in Germany?

Never seen it, certainly would not expect it in upmarket place like Viktualienmarkt in Munich, but have been told that you can do it in Vienna (not tried yet) -they can only tell you no, or something ruder.

Vienna is in Austria not Germany, and the Germans are not really into the bartering over price.

I guess you mean "bargaining" instead of "bartering". The likelihood of the former may be low, but I'm sure is much greater than the latter in the 21st century.