google merchant center underscores and quotes

Should .txt feed files use underscores or quotations-marks?
The answer with respect to quotes generally depends on the use-quoted-fields settings for the registered feed -- by default no quotes should be used; try viewing the feed file within a browser and remove any quotes.
One possible alternative to removing quotation-marks is to change the use-quoted-fields settings for the feed.
As to attribute names, i would use an underscore for any attribute with spaces -- such as product_type; but google currently may accept either notation in a feed.
As to product_type values, i recommend a single google-defined taxonomy per item -- but google products processing currently accepts almost any product_type value; however, the end-results within products-search may not be what you expect so always view your .txt feed file within a browser before submitting the file.
Generally, the Celebird Feed Check is purposefully guarded and strict.