subhajit123 posted:So when making requests in a polite manner can I use would and could interchangeably in sentences like these ?
Yes, would and could can be used interchangeably in making polite requests. As a native speaker, I tend naturally to use could in such requests when I am out in public and actually making such requests in circumstances that are not very formal.
I find would to be a tad more formal and/or serious than could in such requests, but that is something that could easily be debated among native speakers. I do use would occasionally in such requests. You are right that can is less polite. The same thing could be said about will, which is also possible.