This is a huge problem in most digital industries. I did a Degree in Digital multi media and business computing, basically I studied all forms of digital product you can sell. But in most forms non of it is physical. So people do expect it for free.
Togs get s**t on, programmers get s**t on and designers get s**t on.
If you are freelance in any part of the digital industry its very dangerous.
In uni we would be hammered with requested to do work where the client would expect it to be free but then we would invoice them and get a nasty phone call days later.
We once built a website for a country park type place. full process start to finish. 5 sample products built then the final site with 100% original images, logo design, database back with independent server. they stated at the start of the process they had a £15k quote from a corporation with stock images but they couldn't stretch to that we invoiced them at £2k. They never paid. We waited for the hits to start and roll in to the site, dropped the site and remain legal owner of the URL.
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For this reason, I work in retail management.