My huge pet peeve: when authors either do no research or decide that they had better write for an "international" market.
Case in point: I read a few sample chapters of a zombie apocalypse novel set in Australia. It started off with the twenty-something heroes coming back from a holiday (Me: "Oh cool, I know that area!") and then....
-they mentioned how delightful the weather had been during their 'vacation' (we generally use 'holiday')
-the weather had been in 'the high nineties' (I went "what?" before I realised they meant Fahrenheit! No! We use Celcius here!)
-they decided to pull in at a 'gas station' (no, Australians use "petrol station". Or "servo".)
-to buy 'gas' (no, 'petrol'. Unless you're driving a vehicle using LPG.)
- they needed 'gallons' of the aforementioned 'gas' (no, we have been using the metric system since 1967, and petrol is sold by the litre.)
-upon realising that bad things had happened while they were away, they decided to arm themselves from the 'gas station''s gun and ammo display."
That last one? NO. REALLY JUST NO. Look up Australia's gun laws some time. Petrol stations do *not* sell guns and ammo, at least never where I've been. I admit I've never been in the deep outback, where it's vaguely possible; but arms are NEVER on open display! Our heroes would be better off heading to the local Bunnings (hardware shop) and stocking up on shovels and axes.
and that was all in the first chapter! I didn't bother paying the $1.99 for the rest of it.