"You can only flip a property for 20% profit."

[Herm M.]

What does this apply to? Obviously flipping properties.

But what does it mean?

So if I buy a property for 500k and put no work into it... I can only sell it for 600k? According to which lender's guidelines? Which lenders don't have this guideline? Is the guideline irrelevant after 90 days, regardless of lender?

What if I buy a property for 500k, then spend 100k on it? Does that mean I can now sell it for 720k?

I guess my question is... are most lenders lending strictly on appraisal right now? Or are they limiting an investor's profits?