Just a quick question.

Can a newly married Thai wife come to the UK on a visitors visa for 6 months rather than a spouse visa without been asked why she is not coming to the UK on a spouse/settlement visa

The reason for asking is the fact the the lady in question wants to do the listening and speaking exam in the UK rather than looking to do the course and a exam in Thailand and obtaining the spouse/settlement visa

I tend to think that it would be ok because anyone can come into the UK on a visitors visa if they meet the criteria

Yes she can apply for a standard visit visa though, as you say she will need to meet the criteria, affordability, reasons to return and the like, just because you're married it wouldn't be assumed that she wants to settle in the UK.

She will need to satisfy the Entry Clearance Officer that she's a genuine visitor, might be difficult, though not impossible, if she hopes to stay for six months.

You're probably aware that she will need to return to Thailand to apply for a Settlement Visa.