Effectiveness of 100%, 110% and higher guarantees?

[AOCenteno]

Background Info:
I'm not selling a digital product; my product is custom-made clothing that requires the customer to design the garment along with enter their measurements. I am focused on the US right now, and brought up the guarantee question because I want to create a risk free environment for my customers.

The Problem:
The business model is new here in the US, and many people find it hard to believe you can get such a great fit/well made garment with you taking your own measurements. People are just hesitant to try.

Possible Solution:
Offer a 110% guarantee (vs our current 100%) - the extra 10% for their time if it goes bad. The studies I have read show that guarantees are rarely acted upon by consumer; in any case we make damn good clothing with most customers 96% completely satisfied by the original product received. The remaining 4% percent we either pay for alterations or rebuild the garment.

My Question to You all
I want to hear your experiences, especially if you notice a pick-up in sales when you offer a 110% vs a 100% guarantee. In "The Four Hour Work Week", Tim Ferris talks about a 200% guarantee.....I think this may be extreme, but I would like to hear real world experiences with the different types of guarantee out there.