Something don't add up here......when u go into interview, u did not have a faint idea what would be your expected salary that u would accept? And, interviewer did not ask you what is your expected salary for them to benchmark whether that is within their budget?

Your statement, why limit yourself, which mean, it can work both way, they might offer u something lower than your current one.

I don't see any issue providing them the payslip when they request, but, when they decide to give me 20-30% increment max, rather than what I asking or agreed upon, then, I would politely decline as they not paying what the market rate, but, trying to "low-balled" me.

Unless you are not being honest with what you get paid now, therefore, u reluctant to provide them the payslip.

As matter of fact, yes, I do.

My view of salary negotiation is I myself and company come into conclusion what is the "fair" compensation for my experience and skills, regardless of what is my previous pay. So, if either party do not come into such agreement, I would politely decline the offer.

If you goes into the negotiation with the above said mindset, unless you inflated your last drawn salary, then, u got nothing to lose to demand whatever you think you deserve.

If they just offered u 20-30% increment, you can just walk away, declining the offer, nothing to lose. But, if they agree to pay what you expected, you got the job. But, now, by not providing your last drawn salary evidence, u totally blew away the opportunity. Are you telling me that you more than happy to accept current salary which is lower than your "expected min" 20-30% increase?

That's is what you perceived 20-30% increment. But, since you did not agree to provide your current payslip, and they decided to not offer you, you just lost the opportunity to find out.

It work both way, it might be true that they would just offer 20-30%, then, you can just politely declined, cited that the 20-30% not worth the risk you would need to take, or they might offered you something within your expectation.

The moral of the story, you lost the opportunity to know the outcome.