I'm interested in an LG-105 LaserGrip for my S&W 642. I can order it from the Crimson Trace website for $209 or I can order it from an Ebay seller for $157. The Ebay seller has many sales and very good feedback, I'm just wondering if I'll be voiding a warranty or something if I buy on Ebay. Anything I should know or be careful of?