Assuming that you left last season on good terms, the new guy ought to be willing to match last years' pay. Sure, you can give him a week or two, at reduced pay, to get back up to speed, but....
If the guy is a "cheap charlie" who simply delights in having you over a barrel ... I'd grin, bear with it, and keep my eyes open as the season gets rolling.
How to tell? Well, a few weeks is plenty of time to see how this guy operates. You're not the only one on 'probation;' so is he. Watch how he treats others- that's how you will be treated.
