I have dealt with Jesse at Cermark. He's a fellow modeller, and not a bad guy at all.
I do not think refusing to replace a model that the owner tore the wings off by overpowering it is bad customer relations. It's just REALITY. Cermark is not Great Planes...they cannot afford to give away a bunch of airplanes in the name of customer relations and still stay in business. I'm sure they would have no problem with replacing one if there was a problem right from the factory, but putting a 150 in a plane designed for a 120, tops, is NOT a factory problem.
And you all KNOW that a YS 120 is easily the equal of a Saito 150. The YS engines are much more powerful than anybody else's.
Jrbrunt, your post is right on the money. Patrick designs his planes to be LIGHT, and that is a major part of the performance. You can't build the plane to take the stresses of an oversize engine and still expect it to be LIGHT. If it was an overbuilt clunker, you would not have bought it in the first place, right?
I have seen Dave fly his with a YS91. It would do anything in the book.
I have never heard of ANYBODY tearing the wings off of one of these with a 91.
You also are right in saying if you want to go outside the manufacturer's recommendations, have at it, but you'd better strip the covering off and reinforce it properly. And several pounds later, you will have a very different flying airplane than what the designer intended. But that's up to you.
I remember Cermark getting slammed on the old RCO, too. By a guy who had gotten a used ARF as a gift. The guy was smeared Cermark for not giving him a free missing part, though he could not provide any receipt, and the kit was discontinued, and the guy clearly said that he had gotten it as a gift, though he would not say where the gift giver had gotten it from(a swap meet, most likely...if it was NEW, they would have had a receipt.)
It was the usual internet dogpile, a bunch of people slamming them, most of whom had never actually dealt with Cermark.

As far as bad customer relations goes, I think you reach a point where the customer just wants to take no responsibilty for their actions. They just want a free new plane. And a small company like Cermark just cannot afford to do that. How do you really know when it was your fault or the pilots? How do you REALLY know that the pilot did not just strain the plane through a tree? My point being that there are too many unknowns to give all-encompassing warrantees on model airplanes.
Think about this. You own a model airplane company. Some guy says he tore the wing off his airplane and demands a new airplane. He tells you he used a larger engine than you recommended. Would YOU send him a new plane? One that cost you at least $250-300 to get here from China? It's not free, and they are certainly not all profit, so it IS costing you money to give him the plane. Would you REALLY do it? Knowing that it was really the customer's fault?
Awesome, as far as lawsuits go, if something really bad happened, EVERYBODY would get sued. Ask Kraft about how THEY got sued when somebody crashed their plane into a spectator at Shea Stadium back in the Seventies. Even though it was clearly pilot error, everybody who had any deep pockets whatsoever got sued. Just how it is.
I do know that if I were Cermark's lawyer, in such a case, the first thing I would say is that the plane was powered way beyond what was recommended.
You know something, there is this nasty trend nowadays for people to blame anybody but themselves for their actions. I don't think anybody in 1960 tried to get a new free AstroHog from them when they tore the wings off their old one by putting in too large an engine, but I may be wrong...
The GP Pitts, I know nothing about.