Welcome aboard.
With used boats, condition is king - even over brand. Do some reading
HERE and use that to see if this Mariah is a good one. I don't know Mariah's particularly, but I wouldn't be afraid of one in good shape. Well kept, it's nothing "amazing," but it's probably a decent boat.
Just a note: a ski boat and a wakeboard boat are two different animals. Ski boats are designed to lay down a nice level table of water to ski on - low waves. A wakeboard boat is designed to dig into the water and chew it up to make big waves (wake) to board on. AND ... this boat is niether
It's an open bow run about. It'll pull a skier, and it'll pull a wakeboard just fine - but it's not really a dedicated tow boat.
What year is the boat you're looking at? Do you have a link to the ad?