[ResearchAtPlay]

Voluntary carbon markets typically trade in both avoidance and removal (i.e. sequestration) credits. Since this site is called Carbon Dioxide Removal I would assume listed trades only cover sequestration, and my cursory review of the listed removal methods appears to confirm that only sequestered carbon trading is listed (but the methods section does not state this explicitly).

Regarding "is it paying for stuff that would have happened anyway, or is it somehow net removal?": One of the requirements for generating carbon credits is additionality, i.e. a project should only receive carbon credits if it were not viable without the revenue from those credits. But as you point out, determining additionality is rather difficult and often fuzzy.