First, let me be clear that I'm not defending or condemning anyone, as I don't know 100% of the situation. But maybe I can offer my take on what
might have happened.
Most sellers, over time, will be able to predict an outcome based on past dealings with the thing that is "human nature". When an individual approaches a situation, typically it starts out from a "neutral" position colored by whatever expectations they may have based on the sellers' reputation. Obviously, if those expectations are very low, an individual would typically decide to go elsewhere unless there were perks involved, such as a lower than market value cost, or similar.
I think what may have thrown up the red flags was the amount of time he had already spent with you prior to purchase and perhaps the feeling conveyed, after the fact, that you were wary about doing business with him, based on the experiences of another individual. At that point, it's not a stretch to surmise that you might already be expecting to find a problem with his work, before he was given the opportunity to demonstrate what he could do for you. And, as anyone knows, there is no such thing as "perfect", and when one looks hard enough for faults, however small or insignificant they may be, they will be found.
No company can continue to exist by deliberately putting themselves into positions which they believe will lead to failure on their part no matter how hard they try. This is especially so for smaller companies, like the ones who literally devote their every waking hour to servicing a smaller community like this one, and don't have the high volumes or staff to pick up the slack. So when faced with the prospect of probably spending more resources than whatever profit they might make on a sale, to meet what they feel might end up being unreasonable expectations, the only option they have is to let the sale walk. It's not an ideal solution, and perhaps it didn't happen in the best way here, but it can help to keep the lights on and the family fed.
Personally, I don't do this, even to my own detriment. In the extremely rare instance where we have an unhappy customer, it is never one who buys hundreds of dollars worth of components for their "dream" control panels. These good folks have the money to spend, and are buying the highest quality parts, so expectations are usually exceeded. The issues always seem to be with customers with little money to spend, and who purchase as few of the least expensive components possible, expecting the results to perform like full-blown panels with parts costing several times more. As I have personally been in those shoes, I try to be understanding and spend the time to offer guidance, support and ways to maximize what they have, even though the profit from the sale went away after the first of several email exchanges. But it's something I choose to do, and not all are able whilst continuing to be there for the next person who needs their services.
Again, I have no affiliation with Craig whatsoever and don't know him (even though I believe we share the same last name

) but I thought I might be able to offer some insight as to why your experience could have gone the way it did. My advice is "listen to Ark". Buy a flat-pack (from wherever you feel comfortable) and outfit it the way you want. That way, you will have full control over the quality of the end result, and learn many valuable skills along the way.
RandyT