I am verifying the number of available seats from the tableModel first and display a error message if user required seats are more than this number, saying that "You can only book maximum x number of seats on this flight". Otherwise I go ahead with modifying the database. While doing so, I may still find that the required seats are more than the available seats (because the first time I have not considered other concurrent user's reservations), if so then I am displaying one more message saying "Not enough seats are available". I feel this may be confusing to the user. Anybody thought on similar lines ??
Yes, I considered this also. The first message is for when the user you already know that the request is for too many seats. The second message is when their were enough seats a minute ago, but someone just beat you to them. My second message says, "The seats you requested are no longer available". It might be a little more clear.