The give away is always "reseach shows" without any further justification.
"Research shows that 8 out of 10 cat owners thought their cats had the appearance of fewer wrinkes after just 3 applications of Esso super unleaded"
Take 100 salesmen
73% ask at least 5 times
92% of the 73 give up before 5
The 8% is 8% of 73% not of the whole group.
and you're not told how many still get told no after 5 nos
27% get a yes quite easily
and earn 3109% more sales - compared to who? the ones who don't persist? or the 27% who get a yes first time (I know what I'd bet)
This has all the hallmarks of rubbish science
But that's not the point.
You're not meant to analyse this for rigour you're meant to be inspired by it.
It doesn't matter whether it's right or wrong - the only thing that matters is results.
Welcome to Sales!