How do I know if a user has reached my page byhitting the Back Button?

[Purple Haze]

would those variables be processed on the Server or Client side?

[Mr Black]

Server, of course.

[Purple Haze]

That's what I thought. Then how will it even be reprocessed to check for the
mismatched variables? When the user hits the back button, it does not reprocess
all the server side scripts, it just displays the last cached result.

[Mr Black]

You will know that user come from the "Back button" page, when it will be
submitted to you for processing. I thought this is what you want. If you are
truing to control user's action controlling his browser - this is definitely a
bad idea. Never will work reliably.

Imaging that I do not use the Back button, but I am speedy enough and click
quickly Stop and Pay buttons, let's say, 10 times. Will you process CC 10
times also? Or refresh a confirmation page? Users are very "creative".

[MikerRoo]

MTC:

You might want to read some Jacob Nielsen reports and rethink your philosophy.
As a merchant, I want to make it EASY for customers to retry their purchase.

As a user, if someone messes with my back button, I will take my money to a
friendlier site and call up the merchant to give them an earful. The merchant
loses money and gains a terrorist. (Heaven forbid they try to restrict me to
IE).

You need to track states, to guard against accidental double-purchase, but
still allow your vict..., er I mean users, to operate your site in ways that
they are comfortable with.

Regards,
-- MikeR