If they are built to last like the origional ones, people will still buy because everyone speaks highly of them on all the social media sites!
Steve will still have a steady stream of return customers, plus not all window cleaners in the UK are going to buy them in the same month. Hence he will have a steady, ongoing market for them. Especially with all the newbies wanting new equipment etc all the time. In between that, supplying maintenance kits as well plus other little products etc He aint gonna run his business into the ground!
The price is irrelevant, reputation is key
Well thank goodness you're here to sort out his business plan. I mean, it's not like you have no idea what volumes or costs he has is it? LOL! Only he knows what is needed for him to continue production, you are simply guessing.
Also, I highly doubt this has been 'engineered to fail' - that is crazy.
More likely : They used a UK supplier with the first lot as it's much easier to deal with the UK and get answers to questions etc (such as "can this be done in this size/material etc"). UK suppliers are expensive, but they are good quality and can supply smaller quantities, and are keen to help with design tweaks.
Then, when all was well with the design and he knew it was not going to change significantly, then he found a Chinese supplier for as many of the components as possible. It was probably less than 50% the cost of getting them in the UK, but the downside is you need to order a higher quantity.
The problem with chinese components is that the quality is variable, and you don't always get what you asked for. He may have asked for that spring in a particular material and only something similar was available.
The point is, if you have the opportunity to reduce the manufacturing cost by 50%, you're going to do it aren't you? And you won't know about differences in quality for months after you start selling them, and then you have 10,000 sitting waiting to be used up.
Side point - I'm amazed that there were EVER spare parts on sale for this product! I would certainly never have offered them, the product is cheap enough and small enough to simply replace the whole thing as needed. Plus it doesn't look very user-serviceable. I'd have made the warranty at least a year though.