This is just my personal experience when I buy brand new from boutiques: if you go on a
good day when it's not busy and the SAs are
nice, you get to look at several items, try on several items, and have nice conversation with the SA(s). When you select what you want to buy, sometimes you are led to a nice lounge area (if there is one) and, depending on how generous the SA is, he/she may offer you a beverage or a snack. They then ring you up, put your receipt in a nice envelope, and your bag is all boxed up and bagged with a fancy bow on top. It's a nice experience and I'd recommend people try it at least once. You can't really replicate the in-store experience if you buy online, whether brand new or secondhand.
Ditto!!! I dealt with one SA who got annoyed with me because I "only" bought a SLG from him. I was so disgusted with the experience and the brand. Not going to say which brand, but I will say it wasn't Gucci. I've thought about selling that SLG since then because I get mad when I look at it.
Not saying that all SAs are like that (I've met more good ones than bad) but you're likely to get better service if you intend to buy, have a personable SA, and the purchase you make is big.