I worked for Match.com. I can help with some of your issues. You can call customer service regarding the matches. When I worked there a cusotmer would have several ways to search, one method was called "two way". Speak to them regarding your match criteria as well. They're there to assist you.
Match.com doesn't allow anyone who is legally married to join their site. If someone has contacted you who is married you should notify Match.com and they'll investigate and shut down their profile.
Nigerians are a big issue, I would shut down 20 profiles alone in a single day, as quick as I did, they'd open a new one. I found some of the Nigerians that I busted posing as an American on Myspace as well. I mean, with the same picture and exact same wording, ontop of it they tried to get me as a Myspace friend, not knowing I was the person who busted them on Match.com. They seem to be on every site trying to scam Americans out of money, and they somehow manage to find people who hand over thousands of dollars at a time, thinking they are actually helping an American. There's no way to stop it. It's a big problem everywhere.