Now the current employer will say sure we are happy to give a raise. You decline the good job offer. One week later your manager fires you....
That's what actually happened with one guy in my previous job.
He actually came to an office party in the new company but then his previous manager asked him to come back with higher salary offer. He came back and was fired . He was very lucky that our company agreed to re-offer and accept him back
That's why you get the new job conditions in writing, i.e. a new employment contract. If your old employeer fired you, you report them to the Labour Relation Commission (or whatever body is in your juristiction (assuming you're not in the USA, who's employement law is about as good as China's democracy laws))
