Earning something back for real estate transactions is great, and I wholeheartedly support that approach. I will probably get flamed for this, but do consider that there are alternatives to earning miles. In my case, the cashback options is far better than miles.
For example, if you are a Costco member, then have partnered with LendingTree on both buying/selling a home as well as mortgage services.
On the buying/selling side (Real Estate Agent Services)... If you buy (or sold) a house for $500k, the cashback would be $3,700 (plus $100 if you are an Costco Executive member - see link below). Whereas, if you go through LendingTree using the United Airlines promo listed above, you would earn 3,000 miles for each $10,000 of your home’s value plus a bonus of 10,000 miles during the current promo. So, that $500k house would earn you 160,000 miles.... Since I value miles at $0.015/mile, that equates to $2,400. (even if I valued the miles at $0.02/mile, that would be $3,200).
Summary: I would much rather have $3,700 in cash than 160,000 for buying or selling a $500,000 house.
see:
http://www.lendingtree.com/common/bp...9500H000000001
There is also Lendingtree.com and costco deals on home refinancing and mortgages as well. I haven't done the math on these, but my gut says that they too are better deals than earning miles.
see:
http://www.costco.com/Service/MemberService.aspx