Camping coaches and buying kitbuilt locos in BRM

This months' project is one of those that grew the more I dug into it.

My plan had been to take a Hornby generic coach, paint it then plant the result in a field as a camping coach. 

Then I found a prototype and things spiralled. The chassis needed to be replaced with something simpler. The roof line was wrong. And there should be a travelling van as well. 

In the end, the project took more work than expected, but looks, in my opinion anyway, fantastic. 

On BRM TV, I'm taking a look at locos. 

With a growing number of second-hand kitbuilt locomotives hitting the market - if you've never built a kit before, what should you look for in a built-up model? After all, you can't reply on the manufacturer, and will probably never know the builder.