I have sold five single family homes in less than ten days on market since the first of May that were professionally staged. The cost of doing so has been from $150 to $800 per property. Everyone of those has sold at the very top of the market, both presently and historically in what is very much a buyer's market. In combination with previewing competing listings, understanding sell-through rates, understanding the level of severe competition a seller has on the market, and storing unnecessary furnishings as a part of that staging process, staging a home works really well. Alone, staging is an expensive silver bullet. It can't make an overpriced home sell faster, it can't create more buyers in a market saturated with supply. It can help a willing buyer make a decision, especially today as it seems that many buyers who don't want to make repairs, likely don't't have a lot of cash, and likely have tons of options to buy. When that's the case, they will recognize a property that they are viewing as superior to it's competition, and therefore, a better value. But they only do that if they view it and it is priced well. Staging is vital, but it isn't "the thing". Staging enhances "value". Correspondingly, it has to work hand in hand with other key marketing functions, most specifically price.
Something I think that's strong for an agent to consider is the rate of homes that DON'T sell in their MLS. In our MLS (Colorado Springs) only 45% of listings taken this year have sold. If 55% have not sold, do you really want to spend your dollars on marketing a property that is under-conditioned and over-priced, or on something that will help the seller actually sell the property, so that you actually get paid? If the average newspaper ad is $100 and you run that for 6 weeks and the home doesn't sell, versus spend $600 on staging it and putting more money in the seller's pocket and you get paid, it seems that it's a good idea. As a business development tool, a seller isn't likely to refer you to future business for the quality of your newspaper ad, but is very likely to refer you for delivering measurable results (like selling it when the majority don't sell, doing so well below market time, and for maximum dollar).
I've done staging myself of properties, but when it is coordinated by employing a third party, you can more accurately track your expense and the seller seems to buy into the concept with greater enthusiasm, both in practical terms like keeping it looking that way and financial terms by pricing their home more for the buyer's that are looking and less on their improvements and the comments of others that have viewed the home at dinner parties, etc.... but aren't actual buyers.