[Reily]

In those days if you were weaker then your potential customer you traded, if you were stronger a nice sack & pillage might be in order.

In those I doubt vessels were that specialized.

[Pontiac]

A trader would not be able to afford galley slaves for rowing

Here is a link for different Greek ships

http://www.hellenicaworld.com/Greece/Technology/en/Ships.html

The ship was probably a single masted sailing vessel for economic travel

[SunkenCiv]

Piracy was only an issue where there were other ships. As Greek colonization spread, piracy spread, carried out by the local gentry using their local watercraft, whatever they may have been. During the Roman Empire piracy got wiped out and was kept that way for centuries, thanks to their navy and their naval bases, including one in the Black Sea.