I think you should get the Polar attitude that if you extend me it is going to cost you dearly.
Days one and two are 5.47 hours on top of guarantee, plus whatever you are actually flying.
Days three and four are 6.38 hours each. So a three day extension for a typical Captain is worth $2900. Again, plus whatever is actually flown.
Abusive extensions occur, I had a nasty one in November that I am still mad about. However you also have guys going after the money by bidding into trips that are obvious targets for extension (last leg deadheading back from Europe, for example) and/or calling scheduling and offering themselves up. Which is fine, but a few of them then run around complaining about it.