A little story...
A few years ago I fitted kitchens for a while. Quite a few times I'd turn up to a fit where the client, to save a few bob, had told the salesman that they'd take the old kitchen out, but of course they hadn't because it turned out to be a bit more complicated than they'd bargained for (e.g. hidden fastenings, embedded pipework, etc) - so for starters, don't let anyone into your house to remove a kitchen unless they are a kitchen fitter, but then why on earth would a legitimate fitter want a secondhand kitchen? (unless it's a year old and unused) Next thing you'd sometimes get (once they'd taken the washing up bowl out of the sink and removed the wash basket from the worktop) was "the offer" - if you take the old kitchen out you can have it for free for doing the job. Well, no, here's the deal - I "take" the kitchen out my way, you pay for a day of my labour PLUS the cost of a mini skip and I get to work late all this week to make up time and get your fit finished on time so I can get to my next job on the day I promised the next client OR you take the kitchen out and dispose of it at your own leisure while and I go off to my next booked job (early, which delights most people) and I'll fit you in when I've got the time in the future...
By "take the kitchen out", I meant dismantle quickly and skip the resulting carnage, to which end a recip saw and a selection of blades is very handy. There simply isn't the time to do it any other way unless the client is willing to pay for the labour - and for something that will end up on Freecycle or in your back garden for the next 6 months there isn't the time. Fitting a secondhand kitchen isn't much fun either, especially if you end up having to repair any nasty hidden workarounds. They make good garage storage, however