How do I know if a bathroom fitting quote is reasonable?

How do I know if a bathroom fitting quote is reasonable? I'm having a full bathroom refit done and got a few quotes back from fitters — prices vary more than I expected for what seems like the same job (same suite, same size room). A few things I'm unsure about: Is it normal for quotes to include the cost of fixtures/fittings, or should I be sourcing the suite, taps, shower etc. myself and just paying for labour? What's a reasonable day rate to expect for a bathroom fitter in the UK right now? Should the quote separate out things like tiling, plumbing, and electrics, or is one lump sum normal? Is it worth asking for a guarantee on the work, and how long should that typically cover? Would appreciate input from anyone who's been through a refit recently or works in the trade. Trying to work out if I'm being quoted fairly before I commit to anyone. Note : this is the same question we get most often via social media/email at BestQualityBathrooms — customers unsure whether to buy the suite themselves online vs. let the fitter supply it, and unsure what's a fair labour-only price.