I notice the banker most of the time rings the player for the swap pre deal, but i remember in Marcus' game he got the oppertunity to swap at the end after dealing!

No, that was Candice - but she did swap her box with Marcus's!

I don't really like the swap...it just confuses me, and spoils the whole premise of them selling their box. And nobody ever bothers with it unless it doesn't really matter too much anyway.

(Although swapping got Gabrielle £2,000 for charity rather than a mere fifty quid, so I guess it does have its uses.)

But why was it just her then who was able to swap her box post deal?

I think she said "I'd have gone on if he offered the swap" or something, so the banker rang to say he would have offered it. Even though he doesn't offer the swap until after they've No Dealt, so that didn't make any sense...ugh, that ending annoyed me. Another reason why the swap should be abolished!

I think it's quite an important part of making the game fair, as it means that the big prizes are always available in every game. But they need to be consistent in offering it AND not cutting the offer from the broadcast, when the final offer is no-dealt, unless the last two are both blues in which case there's no point prolonging it.

Certain situations (e.g. crap final offer and contestant's box opened to reveal low amount) lead people to suggest the Banker knew what was in there. While there's no statistical evidence to back this up, it does resurface from time to time. The swap offer makes the game appear fairer - though I agree it's unlikely a player would swap away a box they had had in front of them all game and could contain a huge amount, even though it's a 50-50 chance whichever option you choose.