Monitor the market nearest you.

My economics major turned AO addict friend and I discussed this.. I'm not sure if this is normal accross servers or only in Thebes, but you check.

Apparently prices fluctuate and can be predicted based off the time of day. I can say for thebes because i regularly do this.

Prices near the time of 6AM PDT are usually the lowest and are the best time to buy things. Since most AO players put up their wares and go to sleep, Asian players like me get to benefit from the mass underbidding.

At the same time, probably 6PM PDT or earlier is the best time to sell your wares, as wares in the market are low in stock, and people are starting to log on/shop etc.

This is based of experience and server-dependent. But i think its still good information to keep at hand so you can save more.