welcome to the airline industry!!!! You took the risk and had to change, it's like going to tesco and moaning that they said they would still have chicken for sale and you can see it on the shelf, but you bought tesco value and what is left is finest free range corn fed happy chicken.

It's still chicken, it's still on the shelf but it's not the cheap one because it all sold out. You don't know when it all sold out, it could be a few days ago it could be 10 seconds ago. The reality is, if you still want the chicken you have to pay for the chicken they have.

Same with airfares, they are sold in fare codes (usually letters) and as soon as one fare code has sold out they start selling the next one.

The kingfisher agent is probably fully correct that the fares don't normally go up, but how is anyone going to definitively know who is going to book a ticket and when?!?!

So no, they aren't untrustworthy - you just didn't take into account all of the possibilities. If you wanted a fully flexible ticket, you should have bought one in the first place. If you could change el-cheapo tickets, why would they bother to sell fully flexible at a large premium? Still the same class of travel and same seat.

Essentially your argument against Kingfisher is utter rubbish!