1) Yes there will be additional disbursement charges on top of the valuation fees. For traveling, printing, etc.

2) There's usually a discount given on the fees, not the disbursement. But it depends on the size of the valuation firm, the smaller ones are more flexible.

3) You can change the valuer provided they are on the panel of the bank you are obtaining the loan from as well. This appointed valuer is the one who gave your banker the verbal indication of the RM628k, so unless it's a fair market value (and you didn't ask for help to boost the price higher and all), you risk other valuers not being able to value it at RM628k and that will subsequently affect your loan amount.

Hope the above helps!

I believe 30% is possible. You can check with the valuer. My suggestion is not to negotiate so much if they are 'helping' you with the value of the property.