Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Works great but WARNING: might mark or stain your guitar permanently

Dunlop trigger-style guitar capo, "Electric Trigger"This capo works great, but it stained the neck of my vintage electric guitar. It put a dark round-ish spot in the middle of the back of the neck (and also small permanent marks on the headstock where I clamped it when not using it). From now on I will look for capos that have a better reputation for 'non-staining', and I will also remove any capo immediately after playing, to be safe.