i happen to stumble upon this thread...
do remember to ask contractor to give separate quote for box-up. if they r in carpentry work, they should be able to provide a separate cost from the kitchen cabinets.
secondly, if they quoted 13ft and do only 10ft, provided in the contract both you and contractor agree before hand, better with black and white coz scare that contractor may go back on his word (you never know how desperate they can be when they are not earning enough...), that they will only charge you how much they do, den you can ask them to give you back the extras. similarly, if they do more, you must pay them back.
but if in your contract, both agree and sign that the contractor is to bao ka liao, den you cannot claim back from them and neither can they claim from you the extras been done.
and its normal for contractor to hv a small fty nowdays. they will segregate their place for doing different things. eg. cutting of wood at one side, welding at another side, cutting of glass at one side. btw, glass cutting is easy job with the right tools. i don't think they want to risk burning up their fty with messy setups. and nowadays fty hv alot of safety requirements to meet from local authorities, if not its hefty fines and jail sentence for owners/tenants even!!!
and also dun forget to ask your contractor, how thick the cabinet will be, and not juz see if workmanship is good coz i learn from my carpentry contractor that some black sheeps tend to cut corners by giving thinner wood coz quoted at cheap rates for renovation and in days to come, you will find that the cabinet will start to warp, ie. having problems to close the cabinet doors etc.
hope the above helps.