I think he can do what he likes with any of the items he has acquirred on or off the show.
If it is for charity then good for him and if it is for himself then where's the harm?
I'm not surprised the key is at £1,100. the last time I checked there are people out there that will buy certain items if they have the money.
Other housemates are making money off the show in different ways and if Marcus wants to do the same then it's okay with me.
I wouldn't buy it though.