I think the main point of the OP has been overlooked a little - they didn't say people who asked questions were trouble, they said that it seemed like the more questions someone asks, the less likely it is to result in a good outcome. They went on to say that the most needy buyers complain most often, and they are unlikely to have something to complain about if they didn't buy. We've seen this pattern multiple times in threads here over the years. (Someone starts asking multiple questions about something, then they finally buy it and continue asking questions, then they finally pay, then they receive it and there's some kind of problem with it).
The OP is registered in Australia, so we can at least presume they are familiar with the metric system, which also suggests there might be a good reason for something being listed with imperial measurements, but they also had a question mark after the statement, which could indicate the suggestion from the buyer that they had measurements in inches was questionable or weird - people use question marks like that all the time.(eg "They thought I was saying all buyers who ask questions are trouble?"). If I'm interpreting that correctly, maybe they did have metric measurements, maybe it's a small item and the measurements were in mm, or maybe it's a big item and they were in metres.
Some people seem to ask questions for no reason at all (try having the size in large font text on the gallery photo, in the title, in the description, in the item specifics, and then clarified even more in the description, and still getting "what size is this?" questions 
), so if the OP says they are experiencing a pattern with certain types of people who ask questions, I have more than enough experience myself and anecdotes from people in the forum to believe them.
People who feel they need to ask questions about my descriptions don't end up buying because they are too dumb to be allowed to have access to money.
@springyzone wrote:I would suspect that if you have someone who is asking numerous questions over several days, then that could signal trouble. It reeks of either a lack of trust or confidence in the seller or else doubts about buying in the first place. Reluctance to commit.
It can also indicate someone who is extremely particular about what they want, and / or has high expectations, which in turn is a huge red flag that nothing will actually be good enough - a series of questions about every aspect of the item is understandable if they are about to drop a couple of thousand on some custom built item, less so when they are buying a second hand, generic brand tea cup... or something. Or, in other words, context always matters.
In some cases, you're better off asking the potential buyer questions than answering theirs, it means you can cut down on the sometimes seemingly endless back and forth, and really try to zero in on what is the most important info - if you can get them to tell you what they want, it's a lot easier to determine if you can meet their needs or expectations. A lot of sellers will naturally think about getting the sale, and highlight things that are what the customer is looking for, but I prefer to do the opposite and even make suggestions about products I don't stock that might be a better fit for what they're looking for - quite often I still get the sale, so I guess they either appreciate my honesty or had already decided on my item and were just making sure it was going to meet the primary need.
Where I get verbose and ply them with information is when I get questions like "is this hypoallergenic?", because for that one the answer is "technically yes but I will never use that word for my items", so then I feel I have to explain why not.
