Originally Posted by
BigE
In fairness to the OP, it is not uncommon for business to sell/award you a certain product and later give you the opportunity to buy up (both parties can benefit from this at the right price point). It's not unreasonable to ask. But, alas, Marriott seems not to allow this.
But in fairness to everyone else, I've never heard of such a "buy up" with free notel certificates in
any program which has them (not Marriott, not SPG, not Hilton, not Best Western).
Marriott is better, in fact, about extending them (at least the ones you earn from the credit card), which most of those other programs don't even let you do.
In ther travel industry, those "buy ups" tend to be at the last minute anyway. They tend to be "you're here now, would like to get something better than what you've got reserved for a bit more cash?". In the hotel context, it would be when checking in to a hotel, at that point
some hotels (only a tiny fraction) might offer upgrades for "buy up". But you can't use this to "buy up" from one hotel to a different one!
To put it another way, those "buy ups" tend to be offered when the're "excess capacity" they can either have unused or bet a bit extra money for. But that again doesn't apply to using a cert at a different hotel.