@MurphyW, i realise this was not a sit arranged via this site, and note you say you’ll use a THS sitter in future, but please be aware that the best sits happen when both pet parents and sitters are mutually considerate and appreciative.
You"ve expressed dissatisfaction at the ‘service’ you’ve received, and your main issue of contention seems to be that the energy consumption far exceeded your usual costs over the 6 weeks duration of your sit.
You mention thst your sitter had just put a washload on when you returned, despite being asked to use the programme delay. Did you mention this to her, upon witnessing it? Was it her own personal items or the bedlinen, or towels?
You say your home is a farmhouse by the sea and that you asked the sitter to use 2 heaters (you had hoped she’d use one at a time) instead of the central heating, despite that this was a winter sit over a considerable period. Our experience of doing sits in farmhouses is that - unless comprehensively renovated - they are cold and draughty places, even when the central heating is on. To expect a sitter to manage, by using one heater at a time (and thereby limiting any potential for comfort to a single room) seems both unrealistic and thoughtless.
You state that your sitter waited in for an engineer. Please be aware that sits facilitated via THS do not allow for the presence of third parties - including tradespeople - once a sit has commenced.
You say the sitter left 2 beds unmade, do you mean the bedding had been washed but beds not made up? We always strip the bed and wash the bedlinen on our day of departure, but there’s not always time to make it up again.
You also state the sitter dispatched 3 parcels for you whilst you were away. This can be agreed as a favour but please be aware that it’s not an obligstion for sitters.
Your comment of ‘… please respect your host’s requests and be sensible’ will doubtless be considered rude and patronising by experienced sitters on this forum. It really is imperative that hosts clearly state sitter responsibilities in their listings and, since you expect a sitter to utilise just one heater at a time, during winter, this should also be stated in the home particulars. It’s all about informed choice and you’re much more likely to attract the kind of sitters you’re looking for if you set out expectations clearly at the onset.
Of course nobody on here would condone leaving a sit home in an untidy or dirty state, just as no sitter would expect to find an untidy or dirty home on arrival, but it seems there are wider issues at play, here. Good communication and - dare I say it - TRUST, are vital components for a good housesit. This is a mutually beneficial agreement, not a service.
) 2 cats! We stopped because we don’t want to have to leave a sitter looking after our home (they can’t go into cattery for valid reasons) because of the huge electricity & gas increases. I wouldn’t dream of leaving electric heaters for sitters, I wouldn’t use them and wouldn’t expect anyone else to although a log fire……! We use the heating sparingly and blankets but wouldn’t expect anyone else to. I honestly think the answer is not to go away in the winter months….sorry. I think you’ll just have to swallow the elec bills and messy house but I’d give a review if that’s possible even if it’s verbal?
percent agree with 
. I’ve subsequently edited my post to make it more generic, since these issues are still relevant.