My application calls a 3rd party WCF service and chances are that it get time-out 10 in 100 times.
What should i do, should i increase the SendTimeout, are there any downside of it.??
You can't save some investigation. Timeout may be caused by broken connectivity, network overload or server overload. And be aware: using longer timeouts will cause more load on both servers -- your and the 3rd party as well.
Timeout is usually not the problem itself, just a symptom of it.