When they ask for your opinion.

Often, a prospective buyer will turn to the salesperson and ask what they think. If this happens to you, do not, under any circumstances, give your opinion. There are two reasons for this. The first is that your opinion doesn't matter. The second is that you might inadvertently say something that turns them off from buying that piece.

If you are asked this question, simply turn it around, and instead of answering, say something along the lines of "How does it make you feel?" By doing so, you've averted the minefield, and, more importantly, put the onus back on them, moving one step closer to a Yes.