If I ask someone to implement a linked list during 1hr interview, it's clear that it's not because I need a linked list implementation in my company.
If I ask someone to stay for a week to work on the company's code base, that's clearly a work that should be paid for at a market rate.
Similarly, I'm pretty sure that you, as a designer, know without a doubt when company's request crosses the line from "I need to make sure you know what you're doing" to "I need you to do free work for me".
If I ask someone to implement a linked list during 1hr interview, it's clear that it's not because I need a linked list implementation in my company.
If I ask someone to stay for a week to work on the company's code base, that's clearly a work that should be paid for at a market rate.
Similarly, I'm pretty sure that you, as a designer, know without a doubt when company's request crosses the line from "I need to make sure you know what you're doing" to "I need you to do free work for me".