It's always tempting to think garages are trying to 'fleece' you.
You make particular mention of the 'inner wall' (I presume you mean tread depth?) of the tyre. What about the rest of the tread - is the wear uneven? Maybe other aspects of wheel alignment are out-of-kilter - not simply toe-in/out?
Regarding the brakes, 4.5mm pad thickness isn't much. Many owners now go 12 months (or more) between services - how can a garage know the owner's driving style? Frequent heavy, late braking can easily chew up most of that 4.5mm in a year.
Discs are a bit more difficult. Asbestos-free pad materials are harder on discs, which are now seen as 'consumables' - quite often being changed after a couple of pad renewals. You wouldn't fit old pads to new discs, would you - so would you fit new pads to discs that have done 100k miles?
Please don't think I'm trying to defend the truly dishonest garage trade, but sometimes they're stuck between a rock and a hard place.
I have been DIY-ing cars for over 30 years (mainly to avoid garage labour rates), but I do appreciate that garages are businesses - not charities - and must make a profit somehow. Some jobs are beyond my humble working facilities so then I'll 'bite the bullet' and face the fleecers
As regards parts prices. We might have the time to scour Ebay for the best possible deal on some dodgy no-name parts, but many garages will use the same motor factor for speed and convenience - or source from a main dealer for more obscure parts. Even these 'trade prices' can be higher than those offered by Ebay sellers clearing old stock.
When it comes to 'fleecing', how many of us complain of paying £2.50 for a soft drink in a pub when "I can buy this at Tesco's for a fifth the price"?
Think on, Ena Sharples