In my school, EVERY parent knows who the shit teachers are. And every parent without fail groans with disappointment or grimaces when they hear that their DC's have got that teacher next year.
Some of them are very good infants teachers but awful junior teachers, and some are very good junior teachers but awful infants teachers. And this school has a habit of shuffling the teachers round to teach infants even when they are not very good at coping with littlies, all in the name of 'professional development'.
Which is crap if YOUR DC gets them during that year!
DS1 this coming year has a teacher well-known for being shouty and nasty. Properly nasty. But I have explained to DS1 that she is a better junior teacher than infants teacher (he also had her for part of Y1 and hated it), and that if he quietly does his work, he should be ok.
DS2, however, has a teacher that ripped up my DD's friend's maths book when she didn't understand the question and got it wrong, and called DD's friend 'thick' in front of the whole class, and actually SWORE in front of the whole class on that occasion. I am not looking forward to the possibility of her doing that with my DS2 who has LD's...
Neither of them got the teachers I wanted them to have.
After 8 years at a school, and your 3rd DC going through the school about to start Y4, there aren't many of the teachers that you don't have personal experience of, and the few that you haven't, your friend's DC's WILL have had IYSWIM.