Any name not already used in a .com web site name is probably not trademarked.
Good luck, you might find it expensive to get the site rolling, some professional site flippers would pay participants to give it a lived in feeling or copy scraped content from similar sites.
You might search for something like Craigslist Clone script for ready made sites that could save you a lot of development expense.
Ok based on the number of names out there already registered you will probably have to choose
aksdfhsakjbgdjgs.com
I am not joking, why do you think so many companies have silly names
Ok so here are some tricks to get around it.
Use a sentence or phrase, it is easy to register and remember. Just off the top of my head.
BuynSell.com
WeSellForYou.com
EZTrading.com
etc
you can have fun with grammar
Sellersize.com
Tradinator.com
Tradinize.com
Or you can just be obscure.
SmithStreet.com (becuase you are based on smith street)
PurpleClouds.com (because you did too many drugs in your youth)
Riubuysell
It really depends on your merchandise so you can think of a catchy name relevant to what you're selling.
Hal Smith
URLdreamer Consultant
I desire to start a buying/selling/trading website where people can sell and trade the items they want.
Can you guys come up with some fancy names. I want names that will help out the SEO.