I am surprised that people "know how much it is going to affect" them.
I presume they are the crystal ball holders.
I know of no one, who knows for certain how much Brexit will affect them, and in that I include a friend from Latvia, now living and working in the UK, and several Brit friends in France. I also know on less intimate terms, owners of two businesses, one large and one fairly small but both export to Europe (and import from the continent too.) They have made contingency plans already for Brexit in terms of stock and future orders (if and when it finally happens.) Their EU suppliers and buyers have done the same. Now all they want is for Brexit to happen so we can all move on.
Another referendum would be the death knell of democracy. I think most recognise it shouldn't and won't happen.
Voting again whether we leave or stay