this has strayed off topic a bit
Any form of voting is open to abuse, voting at polling stations suffers too. The trick is to keep it within limits not likely to affect the overall result, which could be a problem in marginals, and of course, it is those very seats where elections are won or lost. The system we have may not be perfect, but it does have a pretty good record overall. Until we move to a system of vein identification (it is coming) it will do.