A bit of anecdata: my second software only gig (started in IT) was offered a very lowball rate with a '90 day eval' to bump my pay that came and went. 12 weeks isn't 3 but it took getting another offer to get a raise I more than rightly deserved. I was killing it and everyone knew it.
While 3 weeks sounds like a very short evaluation period, there very much could've been an arrangement like this. I hesitate to use the word 'unethical' primarily due to how pervasive Hanlon's razor really is. She gave them 3 weeks of seemingly extremely productive work and gave them a taste of the caliber of developer they could hire if they just threw enough money at the problem but it sounds like they didn't learn. Every experience like this is a chance to learn something but some companies just fold churn into the equation without properly evaluating what they could do to prevent it. Usually its those companies that think developers are just equal cogs capable of performing all the same tasks at the same magically high productivity level. They rarely learn that you sometimes actually do get what you pay for.
While 3 weeks sounds like a very short evaluation period, there very much could've been an arrangement like this. I hesitate to use the word 'unethical' primarily due to how pervasive Hanlon's razor really is. She gave them 3 weeks of seemingly extremely productive work and gave them a taste of the caliber of developer they could hire if they just threw enough money at the problem but it sounds like they didn't learn. Every experience like this is a chance to learn something but some companies just fold churn into the equation without properly evaluating what they could do to prevent it. Usually its those companies that think developers are just equal cogs capable of performing all the same tasks at the same magically high productivity level. They rarely learn that you sometimes actually do get what you pay for.