We gave a lifetime warranty for about 15 years. There's a few things to know about it:
1. Few ever call with warranty work - mabe we're just that good.

2. Your wording needs to be good - are you covering all labor? What about your electricians labor - plumber - HVAC? Be carefull here.
3. Its a great selling point until you get someone that takes advantage of you - in their minds every problem is the result of labor/installation.
On freebies:
1. Only past customers
2. Never announce it ahead - finish something for them then send them an invoice describing what you did and the cost. Then line item "Thank you for your past biz" or "the referral" - whatever - "Zero Balance Due".