I’m not an anarchist but I’d like to elaborate on your question.

In a competitive economy (big disclaimer), especially in the case of plumbing which has a low barrier to entry, you and the plumber don’t have a significant power differential. You need a plumber, but you don’t need that specific plumber, and the plumber needs customers but they don’t need you specifically. If a bunch of plumbers got together and said they won’t work for you, it wouldn’t be too hard for someone to learn the trade and break the monopoly, in the same way, you could try to boycott the plumber, but they could just find other customers.

But that’s in the theoretical case of like, the free market actually working. There are lots of ways in which it can go wrong. If the barriers to entry are higher, then it’s easier to form a monopoly, and in some industries that barrier is naturally higher (say, microchip production), and it’s also possible to raise the barrier of entry if an entity gets powerful enough to influence policy - for example, if you had to obtain an expensive license to be allowed to practice plumbing. So it’s really two questions: is trade inherently explotative, and is trade potentially exploitative?

Boycotts are sometimes idolized as a way to prevent bad behavior without the involvement of the state. But this is problematic for two reasons. The first being that boycotts are difficult to organize and only sometimes effective. The second is that to the extent that they are effective, they’re not always used to do good things. To use an example, we can look at the Jim Crow South. If I own a business in a town full of racists, and I try to run my business in a non-racist way, then I’m alienating a bunch of my racist customers and racist businesses may refuse to serve or do business with me, until I go bankrupt or am forced out of town. This problem was only solved through federal intervention through the Civil Rights Act.

Under those circumstances, it’s difficult for me to imagine how anarchism could work. As a trans person from the southern US, decentralization and giving power back to local communities sounds nice on paper, but like, have you seen these communities? Have you looked at what they’ve done historically when federal authority was looser? Who is poised to take power in those regions in the event of the abolition of the federal government?

That doesn’t mean that anarchism is fundamentally unworkable everywhere, though. It just means that you have to evaluate the actually existing material and social conditions and figure out what can be done where based on that.