I tend to ask the shop owner/bat maker for their recommendation initially
Then try the pick up, play a few shots etc with what they have put forward
Then for me, I have to bounce a good quality ball on it, ,I know a lot prefer a mallet, but I play cricket with a ball,not a mallet.
That to me, is gonna give me an idea of how long the middle/sweet spot is, and if the sweet spot is centralised or not
Two of the best bats I've had regarding long and wide middles,(ace, and a gray nicks) were both not the prettiest looking bats, the Ace bat was a grade two bat. The GN bats middle is huge, still the best bit of willow I've ever come across.
I think, cost does come into it a little bit, ,but if that perfect bats there in front of you, ,it's very hard to say no to!ha
As regards trusting a bat makers choice, hmm, suppose so, , I had a laver made, that was ok after removing three ounces of it
Had three M&H bats,which have all been well below my expectations
But then my Affinity,(made from what Marcus recommended) is stunning .