Upgrade cost for exchanging same size units

I recently went to Trading Places to trade a 1 bdrm unit, in a 5 star resort in Purtea Vallarta, mx for a 1 bdr unit in Park Cities, Utah, with a 1 Bdr, that slept 6 versus my unit that sleeps 4, they wanted to charge me an addtinal $ 100.00 for this unit.Has anyone had any dealing like this and if so what was the result? I have traded through Interval and never had an issue and have upgrade to 2 bdrm for no addtional charges.

Leroy