LemonThrower-
My situation with H. Stern may have been a little different- I had seen a specific design of bracelet (a "rainbow" of semi-precious stones graduated in color) 20 years earlier in their ads in the NY times and I wanted THAT bracelet. Since jewelry is one of my vices, I also have an idea of what something should cost when I look at it. I paid $1,000 for the bracelet; a jeweler in the US with whom I've done business many times appraised it at $2,700. So, I'm happy.
I do advise that you avoid the caiparinha they offer you while you're deliberating, though!
Good point about getting a guide for Corcovado. We took a group tour arranged by the hotel and were VERY grateful we didn't try to drive up there ourselves. Very steep road, limited parking. Take the cog railway or leave the driving to the experts.