I think many people are being unnecessarily hostile and suspicious here.
Private house concerts are quite popular, and many artists play these kinds of concerts on a regular basis. (Whatever you think of her playing, Lola Astanova's career was launched by private concerts - a rather creative route that ended up being far more successful than beating her head against the wall on the competition circuit.)
The few private house concerts I've been involved in were fund-raisers. People get together, have some wine and hors d'oeuvres, listen to some music, and politely discuss various institutions they'd like to support. (The fund-raisers I've done were for a regional symphony and a public library.)
To answer the OP's question - the best way of getting an artist booked would be to contact the local Steinway dealer, most of whom keep in touch with those who have purchased pianos. Another way would be to offer the artist's services for free or a discounted fee in the interest of fund-raising. In this case, it's best to pick something local. I've found that most people who have money, nice pianos, and houses are very interested in giving back to the communities in which they reside. A concert is often a way to bring those people together for a good cause.
And they'd much rather come together for a good cause than give money to an artist they don't know just to show off their house and piano.
"If we continually try to force a child to do what he is afraid to do, he will become more timid, and will use his brains and energy, not to explore the unknown, but to find ways to avoid the pressures we put on him." (John Holt)www.pianoped.comwww.youtube.com/user/UIPianoPed