Shoe advice - am i being led up the garden path?

Like many things, I'm probably over thinking this, but...

I'm relatively new to trail running, having just signed up for a 15km trail race in October. At the moment I'm just running in my road shoes - but have decided I need a pair of proper trail shoes now. When I bought the road shoes, they were my first pair of proper running shoes, and in that process I discovered I really badly over-pronate, and that was what was causing my ankle pain. Buying those was amazing, and totally changed my running experience - genuinely helped me fall in love with it!

Anyway - I went back to the same shop this evening and picked out a couple of decent and supportive looking trail shoes to try (this one and this one). I asked to try them on the treadmill to see how they dealt with my over-pronation, but was told: a) I couldn't try them on the treadmill because of the grip on the sole. b) this same grip / tread pattern meant I would not over pronate anyway, because 'the structure of the sole won't let you - it's just too grippy'

I argued the point a bit and then gave up.

Does this sound right to you guys? Are those even the right shoes to be considering anyway?

Thanks in advance :)