If an employer asks how much youre previous job pays, can they check if you lie?

That is one of the few check points most states do allow in a former/prospective employer check. There is a very limited amount a prospective employer can inquire to from a past employer. That is on the up and up. I was talking to a manager once. Because it was rumored that a very feck employee gave him as a personal reference. He told me, that was a mistake, that he thought he would lie for him, or maybe thought that listing the production manager as a reference would get him the job. You see, there are things you can tell as a personal reference that you can not say as a manager, a representative of the company.
Wages can always be checked though. Reason for being fired, or even the fact that you were fired can't, in most states.

yes

If you lie and they employ you then it is very easy as they know from your tax previously paid........and you will be sack.....of course they can ask your previous employer who can tell them and most industries know their salary norm anyway

Sure, all they have to do is call the former employer.

Yes they can. Probably not through your company as there's all sorts of data protection etc.
But by simply saying "hey, want the job? Then lets see your wage slip ....for admin purposes."

In the US, it is pretty simple to do, by checking your Social Security Number, which will register the payments made. From that they can determine your prior salaries.