No - customers don't share any responsibility.

I just opened my last sack of King Arthur flour, which I learned about here. It costs more, but I feel good knowing that I am supporting a business where workers are treated well. I also pay more for eggs with a Certified Humane label. I know I am not saving the world, but at least I can do the best I can to make my contributions support better practices.

Do you think my shopping habits make no difference, or they do make a small difference but it's the government's responsibility to ensure good business practices so I should stay out of it? Usually it's the libertarians who get blamed for saying "I took care of myself, it's not my problem to worry about others." Do you really sense no tension when someone blasts Amazon for not spending more on employees while also paying $120 a year to be a VIP Amazon customer, citing their low prices?

If one corporation is undercutting others by paying its employees less than living wage and selling inferior products, and also using this to put their competition out of business so that there are no alternatives, that is the fault of the corporation, not the consumers.

I do agree it is the management's responsibility to choose a business strategy. Both of the practices you mention would put a business at a disadvantage. A business that pays better wages will get first pick among employees, and a business selling better products can expect to ring up more sales.

The cheap strategy can work if the business passes their savings on labor and quality to customers. Keeping prices low is exactly how Walmart survives while Costco sells better merchandise and gives employees better compensation. (It seems that Walmart actually gives their employees a bigger portion of the revenue they earn for the company than Costco, despite paying lower average salaries.) We should also remember to include the savings enjoyed by the customer (in the case of Walmart, typically a less-affluent demographic) as a positive.

public transportation is a public good

I can never remember these things so I had to look up the definition and public transportation does not meet the two criteria of public goods:

Non-Excludability: it is possible to keep people out who don't pay for the service; that is what the turnstiles do.

Non-rivalrous: when one customer takes a seat, no one else can use that seat.

It's still possible to argue that low-cost public transportation is an important ingredient in social health; and you mention many plausible benefits. Maybe an abstraction like "efficient urban transportation" is a public good. From a practical perspective, I am skeptical. It seems to me that we spend quite a lot on public transportation, it invariably fails to make any profit (unless you count the contractors who do very well building infrastructure) and requires large subsidies, and also serves affluent customers much better than the poor. I think low-cost, flexible bus service makes a lot more sense, but light rail (and super-expensive high-speed rail) gets a lot more public support. If public transportation in practice worked better at meeting the goals you describe, I would be more supportive.