"The customer has absolutely no obligation to the merchant.
Why do some merchants feel otherwise? That is a rhetorical question. There is no defensible reason a merchant should order a customer to contact them prior to leaving a review, let alone break TOS and harass them for leaving a review."
Actually just like in RL if you purchase something and it doesn't work properly or you can't figure out how to work it the appropriate, adult way to handle the situation is to contact the company and ask for assistance so they have a chance to help and provide you with exactly what you want or need.
Argumentative, rude, abusive behaviour is not well met in RL or SL and honestly, most merchant's in SL don't make enough to have to put up with rude, arrogant people that aren't even willing to let the creator know there is a problem in the first place. To put it in a bit of a perspective, I just bought 12 full perm animations at 5000L$ apiece, that comes to 60,000L$ which in turn if you purchase that amount right now you would have to spend $232.56 USD. The item I am making of course has over 200 more animations, as well as multiple textures, the mesh itself & the 12 to 18 hours that gets put into building the piece, but will only end up costing about 500L$ ($1.92 USD ) for my customers to purchase. If I make a mistake and someone leaves a horrid review without even telling me there was a mistake and I contact them to try and fix the problem and get chewed out, called names, etc. (Had it happen) then why should I have to put up with that? I will bend over backwards to help anyone that approaches me kindly and allows me to help solve a problem, but, I will mute and ban if I am treated badly and then there really will be no customer service given because I won't even know you have a problem.
People seem to think it's super easy and cheap to make things, but, it's not and unless you're one of the elite creators (like the ones that run the subscription boxes that make over $4000 USD a month just from the subscription box alone, not even counting her multiple stores) most of us creators barely make enough to buy more items to build with and maybe if we are lucky make enough to pay for a piece of land for an inworld store, most of the time it takes me about year or more to make back what I put into each product I make and even come close to making a profit, so yes, I think that deserves a little respect and common decency. Customers do us a favor by buying our products, but, it works both ways, we are doing you a favor as well since you buy our products because you can't or won't make them yourselves.
People really need to get in touch with the old school mentality of respecting other people, this entitlement mentality is what is killing the world.