Folding to a check raise on flop or turn w no reads

If I just sit down to a game, and I have no reads on the players, what's the right play when they check raise. I'm playing online poker right now, and I sat in 2 different games where they check raised me. One time I get AQ and lost to Aces and Fours, and I lost another hand w top pair w a good kicker. If I'm no or have absolutely no reads on the person, and they check raise... should I just throw it away most of the time because I'm beat? What's the probability I'm losing? I'm feeling people don't really check raise bluff, semi-bluff, or have a flush draw in low-limits? Should I just fold the hands w top pair on the river if I don't improve? If the probablility that I am losing is over 50% of the time, shouldn't I just fold?