Ask HN: Do you sell first or comply with laws/tax first?

It is a jurisdiction specific question. In some places you need license(s) just to operate as a business.

In most cases it is better to incorporate and do all the necessary registrations before making sales. But if your product/service doesn't take off as expected then the up-front costs are in vain. Some persons are comfortable with the risks of operating as a sole-trader.

can't they pivot to other products/services if the sales don't take off? Or will they break the initial agreement if they pivot?

Comply with tax and other laws first. To do it the other way around is, in my opinion, completely unethical. Even ignoring that lawbreaking makes the company literally a criminal organization, a willingness to do that indicates a kind of fundamental flaw that makes the business forever untrustworthy to me.

Comply first. Otherwise, you won't have a business bank account where you could direct the money from the first sale.

what to do if business doesnt take off?

Hire an auditor who confirms that (based on the lack of transactions and invoices), then close the company and all accounts.

It probably doesn't matter if you're a beginner.