Plenty of hard work transparently advocating for the most ridiculously unpopular policies possible. To name a few examples:

• He advocated for an end to the eight-hour workday.
• And for raising the retirement age.
• And for weakening layoff protections for workers above age 53.
• He thinks that health insurance shouldn't cover dental work even if medically necessary. Maybe because he thinks that refugees take up all the appointments (which there is no evidence for).
• He wants to make Labor Day stop being a holiday.
• He strictly opposes UBI.
• He insists that a wealth tax is inherently unconstitutional. It's actually explicitly mentioned as valid in the constitution but currently inactive due to a deliberately ignored flaw in one paragraph.
• He campaigned on banning cannabis again.
• He thinks climate change doesn't need to be addressed too quickly since "floods will happen anyway".
• According to him, eco-NGOs like Greenpeace should show greater appreciation for the free-market economy.
• When a law was passed that required top politicians to disclose their side income, he tried to stop it with a lawsuit. It turned out he had side income from 14 different sources.
• While the insists he doesn't like the AfD he still regularly uses their talking points and rhetoric. He'll also happily team up with them if it gets him a majority.
• He blatantly kissed Israel's ass after they attacked Iran and, when Germany suspended arms sales to Israel over human right violations, worked to get them restarted ASAP.
• When the ICC issued an arrest warrant against Netanjahu, Merz said that he wanted to find a way for him to visit Germany without being arrested.
• Speaking of wars; after Ukraine was attacked he complained about Ukrainian refugees supposedly traveling back and forth between Germany and Ukraine and compared them to tourists.

That's not all of it. That's just what I could think of/find at the moment. That man is determined to torch his reputation.