I've got clients very close to the threshold who do just that. It's why a lot of small businesses open "short" hours, or take a few weeks' off each year, etc., i.e. so that they avoid the VAT trap without breaking the law.
One client is a guest house who simply closed the top floor to reduce the number of letting rooms from 9 down to 6 to stay under the threshold. It means overheads are less, i.e. less utilites, fewer staff hours for cleaning, smaller laundry bills, etc. We crunched the numbers and he's better off doing that that breaching the threshold, incurring additional costs and losing the VAT on ALL his turnover, not just the excess over the threshold.
Another is a small bakery/pie/sandwich shop. By only opening 3 days per week they can stay under the VAT threshold legally. Again, it means smaller utility bills, lower staff wages bills, and less wastage. Again, we did the number crunching and it makes perfect sense as again, they'd lose the VAT on ALL turnover not just the excess.
A final example is a fish and chip shop who close down for two months per year to "break" the 12 month rolling turnover threshold for VAT.
All three "could" break the law and not declare cash takings, but have chosen to find other ways to avoid VAT registration.
If tradesmen want to break the law, then fair enough, but let's not pretend otherwise - it's illegal and if they're happy to break the tax laws, I'd put money on them not being too bothered about other laws either! I wouldn't want such people anywhere near my house nor car.