Flexor the Mighty!
18/100 Strength!
Well for starters with a roll of 7 total my description of the result would not be as simple as "you find nothing" - almost none of my "describe results" are that simplistic. i would observe that their search found nothing but add in bits of this and that to show them that they are not clear and confident that it was a full good search. there are numerous things presented already to illustrate this. One of them might well be that some things rattle when picked up.
If players followed up on those to do more specific, more destructive things, then the results would have a chance to chenge - just like how a locked door can be attempted to get past with skill (pick locks), muscle (force the lock) or by simply destroying it. Simpkly destroying it is an option.
The catch of course to your "smash the goblet" is the result of "it contained a fragile macguffin, now destroyed" just like the "kill the door" approach comes with its own "cost for certainty" attached.
The underlying question for balance considerations is "does the narrative fiat strategy" produce such demonstrably better outcomes than the "character skill approach" or not, and in the case of the smashed goblet and the killed the door examples, the answers should clearly be no often enough to not make this such a well advocated strategy for more success as some choose to describe their other auto-success impacts on play.
I'm assuming that the McGuffin isn't breakable, its a large metal key for example. If it was breakable of course you would smash the fragile object hidden inside when you smashed the glass globe. In that case assume the player says he wants to boost the halfling up there so he can take the globe down and they look inside it, where the DM had put the item.
I was just wondering how far do DM's go to limit the potential results of stated actions by the players at the table in favor of the result of the dice and the numbers on the sheet. I like it when my players are clever and out-think me, though far too often they don't even try and reach for the dice. I'll give out bonus XP for that usually. To me engaged players using their creativity to solve problems outweighs sometimes a player being more clever than his +5 bonus would indicate.