A local radio station constantly plays an ad from a local real estate agent. In the ad she claims to sell 20X more homes than anyone else in the area, and that, “If your house doesn’t sell, I will buy it from you!”
Sounds scammy. What’s the catch?
I’m sure she’ll buy it from you, but not at full market value.
“If I don’t sell your house at full market value, I will buy it from you at a significant discount…and then sell it at full market value, pocketing the difference. This in no way incentivizes me to do a shitty job of selling your house the first time around - honest!”
There’s a company called Home Vestors who do just this then turn around and sell it to a flipper unless they also flip themselves. My guess is that the RE agent is involved with something similar. We have one in our area who advertises similar.
She will only accept listings that are easy to sell. If your house is the type that is not selling or you are demanding an unreasonable price, she will decline the listing. If for some reason she miscalculates, she can probably move it by reducing her commission. Worst case, she’ll take a couple thousand dollar loss as a cost of doing business.
It’s kind of like the car dealers who say “We will beat any other car dealer’s price or give you the car free!” Why on earth would they give it to you free if all they need to do is lower their price a bit?
Volume
Here is a really good articleexplaining how, in general, these offers work. It can be a scam or it can be a legit way to offer a seller a guaranteed end date, albeit at a lower selling price. The realtor most likely will require the owner to make the home top notch sale ready before listing the house. A turnkey home will sell more quickly than a fixer upper, in most cases. As always, caveat emptor!
The agency cannot force you to sell the house to them. I am quite certain the contract you would sign will simply say that they guarantee they’ll make you an offer. The offer will be preposterously low, so you won’t accept it.
In other words, it basically means nothing. It’s just a way to make the ad sound punchy.
My limited experience is that they guarantee a low sale price. Something below market.
If that price isn’t met, they can feel comfortable taking off your hands and either renting it for awhile until prices pick up or putting a little work into it and still making a profit.
For the seller, it provides comfort that they will have a guaranteed sale, which is of interest to some folks.
Wow, I’m honored you’re using my quote as your signature! It’s like that moment in When Harry Met Sally where Carrie Fisher quotes Bruno Kirby back to himself. My brain shorted out for a second. 
To the OP, it’s already been said, but yes, she chooses the offering price, the owner of the house doesn’t.
Forty five years ago, the owner of my house was suddenly transferred to Toronto. A RE agent guaranteed him a price of $30,000, but gave him 30 days to sell for $33,000. I saw the sign walking to the train station that same day and had put an offer of $30,000 on it the same or next day. Two days later we settled on a price of $31,800 for a house that probably would have been put on the market for somewhere in the range of $35,000 to $39,000. There was a very similar house on the next block listed at $39,000 whose owner blew a gasket when we offered her $35,000. These deals can be legitimate.
Where I previously lived, there was a guy who made a living by offering the owner of every house that came on the market 75% of the listing price. Not many were interested but some were and he would live in them for six months, fix them up and then sell them and look around again.