Is it a mark of the lack of common sense among many FT's who take overseas jobs, sign contracts and then complain how unfair they are on boards such as this ?

I'd have to agree with you on that one.As for the standard contract I mentioned,it was composed by the State Bureau for the Administration of Foreign Experts,and is used widely in China.Usually the particular educational institution you will be working for will also ask you to sign an appendix to said contract.The main purpose of the appendix is to detail the actual teaching to be carried out.

The standard contract,amongst other things,specifies that an FT is expected to 'guarantee the quality of his teaching'.And there is also a clause allowing the FT the opportunity to improve his unsatisfactory teaching in the event of complaints so that his teaching can be re-assessed at a later date.If his teaching is still deemed unsatisfactory then,he can be fired on the spot at once.

So I don't see any need for additional clauses re probationary periods,or clauses pertaining to percentages of students liking the lessons of FT's etc.
Personally,I've always been satisfied with the standard contract(and therefore signed it),but not always with the appendix to it,in which case I'd try hard to negotiate the unsatisfactory clauses in the appendix to my satisfaction,or look for a post elsewhere.Only once did I sign an appendix I wasn't totally happy with.That was because I felt it would be too late to find a college vacancy elsewhere.

If a potential employer offered me a contract other than the standard one to sign,I wouldn't sign.You see,the standard contract has a clause allowing arbitration in the event of a dispute beween the employer and the employee that can't be settled.Said dispute could be about unsatisfactory teaching or not,for example.In fact,no employer wishes to involve the commission for arbitration based in Beijing.So the disputes can be settled fast and amicably at the workplace in many cases.I reckon employers not using the standard contract are trying to disassociate themselves from said arbitration procedure,which can be used by the FT to prevent him being victimised.

I'm glad to learn that the employers you have worked for issue the standard contract as a matter of course!It's a good yardstick,as well as a good starting point for negotiations along with its appendix.