How To Get Consistent Results In Advertising & Grow Your Reputation

I do believe that "actual results may vary" is a valid disclaimer in advertising - or virtually any sales-based project.
The key isn't in avoiding poor results but rather in managing expectations. If you explain that advertising is an iterative process which tests all assumptions a person can make, then it will indeed take a few iterative cycles to dial in the ad/offer/outcome.
Communication is key:
- Set expectations appropriately
- Develop the first iteration and go live
- Measure the outcome
- Communicate results and readjust expectations for client
- repeat
Failure is really a just a matter of when you quit. If Bill Gates quit Microsoft in 1982 then he might have been considered a failure. If he quits in 2006 - he's arguably one of the most influential people in modern history.
When in doubt, try something new and keep on keep'n on!