asp.net - Malicous modification of web page data before Posting to server -

i in process of designing mvc5 web application financial purpose , have security related question.

the example quotation of flow is:

1. user requests quotation server
2. user presented quote £100
3. user submits form accept quote (sends value presented server in post).

is possible malicious user update data maliciously presented them on client (change quote £100 £50) before submit button pressed post data server?

i know possible intercept post request , modify using various tools.

that depends on transport security measures in place, security of user's machine. so, basically, without more information: yes, possible, see mitm more information exceeds so's limits.

edit: question, of course user can manipulate it's own post request, example using developer tools come browsers.

the server should validate user input various reasons can , remember it's original quote. if via whatever way (forged request, mitm, ...) not right, server should detect that.

simply believing users post not enough effort, security-wise.