I was riding on the Berlin U-Bahn (subway) recently and noticed an advertisement from a very well-known auction website on the wall of the subway car that read Trödel mehr als der M41. This use of the verb trödeln had me puzzled, though I knew it was related to the noun der Trödelmarkt:
Also, hier gibt es auch viele Secondhand- und Trödelläden.
So, there are also many secondhand and junk shops here.
Caption 26, Jonathan Johnson - Kreuzberg, BerlinPlay Caption
The noun der Trödelladen has a similar meaning to der Trödelmarkt, just as der Laden has a similar meaning to der Markt. I knew that trödeln means "to sell things at a junk shop or flea market," but what does this have to do with the Berlin M41 bus line? It turns out the slang and most common usage of trödeln is "to go slowly" or "to waste time," but also "to move slowly without a fixed destination," thus "to wander," "to amble," or "to meander." The auction website ad translates approximately to "Wander around (alternately: go shopping for secondhand goods) more than the M41 bus," so it's a play on words on the fact that the M41 is a long, meandering bus line and that you can use the auction site to shop for good deals.
The noun der Trödel, which is also short for der Trödelmarkt, has taken on the slang meaning of "useless, worthless things, especially clothing, furniture and household articles," just as you expect to see in a junk shop or flea market, the latter of which translates directly to German as der Flohmarkt, by the way.
Junk shops and flea markets are numerous in Berlin and range from places filled literally to the ceiling with useless, broken junk to something much closer to fine antique shops. Those people who are too poor to shop anywhere but at Trödelläden and Flohmärkte can take comfort in the wise words of Piggeldy and Frederick:
„Schätze kann man nicht essen, bloß verkaufen.
"You can't eat treasures, [you can] only sell [them].
Caption 13, Piggeldy und Frederick - ArmPlay Caption
„Reich ist, wer was verkaufen kann."
"Rich are those who have something to sell."
Caption 16, Piggeldy und Frederick - ArmPlay Caption
Go to the German Duden dictionary and see the various meanings of der Trödelmarkt, der Trödel, and trödeln, and then see if you can guess the meanings of this list of words relating related to trödeln. Then you can go to Yabla German to find other real-world examples of the words related to shopping in German.