I'm not entirely sure why but this seems a bit unethical to me. It is quite clever but maybe you should make it more clear that you are doing a survey and not actually selling your book.
The only valid signal for willingness to pay is ACTUAL WILLINGNESS TO PAY. Ideally, you'd even collect (and discard) a credit card number. Asking people to take a survey gives inaccurate results
At that point why not just sell the thing? The per unit cost of an ebook is under a penny, who cares if it sold for $6 or $9.. if they pay, give them the download.
There were a few reasons why I chose to say 'This product is not yet available yet' rather than sell it. First, I was going to do a full product launch and didn't want to release the product into the wild yet. Second, as comments stated below, if one person bought it at $100 and realized someone else bought it at $5, they would be angry. They would ask for their money back. If I were going to eventually charge $50 for the product (which I did), the people who bought it for more would be pissed.
You could give it to all your first customers for the lowest point offered. That is, they said they would pay $60 but you only charge them $20. Tell them why. Tell them this is basically an introductory price and it will go up, but because they helped you they are special. Of course, this limits the N you get for your testing, but it gets rid of the ickiness of it all.
It seems unethical because it is. Making what appears to be a genuine offer to sell at a given price then saying "haha, sorry, just wasting your time to help me but without paying you for it, I'm not selling" is unequivocally a dick move.
A/B testing prices. Never heard of that before, seems interesting. I have heard of people creating landing pages to get a mailing list of people interested.
Are you collecting their email's, sending them to a page or social page to check back when your product is available?
Someone picking a higher price, and you end up pricing it lower that sounds like a plus. If someone picked lower then you actually price it, wouldn't they have been false advertised to? Unless they actually knew it was a survey up front then that seems more fair.
A/B pricing has just as good of a chance of destroying your business. Far more "everyday" users than you'd expect will Google your company for coupon codes, discount opportunities, etc. The very moment that someone sees a $20 price for them, and finds out that other people are paying $10-15 - you've just lost a customer.
People like to think they're being clever by A/B testing their prices. The fact is enough people are smart enough to figure out that their "A" slot is worse than the "B" slot you've given other people.
A/B testing prices is huge. In fact it is so common that loads of web scraping products get totally caught out with it (as ecommerce retailers tend to give the best prices to new customers, ie ones without tracking cookies set).
This actually totally broke one startup I knew (that was trying to build an API for ordering products from loads of ecommerce sites).
This goes back to the days of newspapers, classified ads, and late night infomercials detailing how you can get rich from thousands of tiny little ads. One trick was to advertise a product at a specific price, saying "Send in your check or money order for $99 to P.O. Box..." and state that delivery was in 6 to 8 weeks. If you got enough orders, then purchase the product at a bulk rate and fulfill the orders. If not, send the payments back to everyone with some apology. Rinse and repeat with different ads at different price points until you find what generates the most profit.
1. Set up Google Ads for your product to drive some traffic to an hidden web page
2. Set up A/B testing for your product with a range of different prices. I set up six web pages with prices ranging between $5 and $100.
3. When users click 'Buy now', have a page saying that the product is not available but record the number of people who clicked it.
4. Calculate which setup generated the most income.