I designed a slide for the Engel fridge (plus 54 other makes) to go into the back of 4WD's. When I sold my business 4 years later there were 14 other makers of that unit, different materials, but all the same concept. Even Engel, who took 100 units every other month, took a unit to China, to get it copied. The runners weren't up to the standard, and fell apart in our rugged environment. To get it patented in Australia was going to cost something like $100,000, money I didn't have.
I know of a farmer, who lost his farm and over a million dollars in legal fees, just because the patent attorney, (who was Australia's top PA) put in adjoining, instead of adjoining/adjacent. Things only have to be changed 10%, to get away with it, unless it is a concept.
Kryn