I have original watercolor by Martin Kainz. It was painted in 1967 and to me by the artist.
How can I find its value

www.AskArt.com holds 2 records of Kainz' work that have been auctioned in the past; 'Landscape' and 'Floral Still Life'. To obtain online access to these records you must subscribe to the site ($13.50 for 24 hours). Whilst this is no guarantee of future prices, it may give you a 'ballpark' figure.

Clicking on the following search might also be something that you could try as far as finding possible values.

Martin Kainz Painting eBay - Google Search