Couple of points here. While this is going to depend on the player, with a bet like that in most cases he's got more than top pair on the board. And if you're calling a huge bet like this, and lose in most cases, it's not a good idea
On the other hand, the guy might be a dolt, and they aren't exactly rare on the internet

This is going to come down to whether you think this player would go that big with a hand you could beat or not.
As far as the bet of 50 and slowplaying, I agree that this is too small at this point. I'd be looking to go with what I felt opponents would call with a pair of queens. You want to get paid more than just 50 for them to see another card.
KC
http://kingcobrapoker.com