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Buying used paints especially from net is risky. You cant be sure about honesty of seller or his/hers knowledge.
If I decide to buy used paints I ll buy them h-t-h (so see them first and then decide if they are worth it and I can easily decide on the price).
Prince August company has vallejo paints (my primary paints for miniature painting) from 1€ which is probably best price you could find for a new paint pot.
Also there are Warcolors (http://www.warcolours.com/) from manufacturing company from Cyprus which are also concurrent with their prices.
I see that you mentioned 83 paints, that is too much in my experience for a "normal" painting (not counting pro painters, commission ones etc). I think for a start around 20-25 paints is more then enough and after you get some experience you can buy what are missing.

1€ for Vallejo is more then great price. There are some differences between all manufacturers but in the end it is all up to you and your preferences. When I started hobby some 20+ years ago there were only revell and gw paints so I logically switched to gw but few years later when I found Vallejo I switched my whole palette to them.
One of universally high points between GW colors and some of the other companies is so called dropper bottle. That thing makes your life easier and lifespan of your colors longer.