Not at all! You aren’t obligated to tip, ever.
As a freelancer and business owner, I never take it to heart when someone doesn’t tip me. 🙂 I’ve received bonuses on other freelancing websites and tips at work, but I never expect them but do appreciate them. Sellers and business owners should come to understand that buyers/consumers don’t always have the money to throw tips around; tips should be rightfully earned in my opinion.
I agree with you that if you hire someone and negotiate on a price, you are both happy with that price, and a tip is not necessary.
However, if you felt the seller went above and beyond, especially for the price, or you have worked with them before, I think a tip would be nice, but still not expected or necessary.
Just my two cents.
