I am all for this - if you promise top rankings then you must deliver. A promise is a promise, so make sure to be upfront with your clients and promise only what you can deliver.
"The [Washington] state attorney general said yesterday Redmond-based Internet Advancement must pay penalties for failing to get its customers top placement on major search engines. Internet Advancement, which also goes by 4GreatBuys.com, must refund customers, pay $24,432 to the state for costs incurred and a civil penalty of $25,000.
"The company had promised to get its customers ranked in the top 10 to 20 results on the search engines for $980 to $1,500 in set-up fees and monthly fees of $79.80 to $89.95."