I will never knowingly purchase stolen goods or gemstones that have exploited human labour. Most gems I buy are via registered sellers who have impeccable records. The gems I stock are cut in factories in the main, however these factories are run responsibly and ethically.
The rough gems I purchase to have cut are all sourced through gem dealers who buy directly from the miners, or from miners who advertise on websites. Most of these will be artisan miners and they are given a fair price for the gems.
I will not purchase any gemstone used to finance human suffering. This would include child labour, or forced labour. I get to know the dealers before buying from them and choose my suppliers carefully based on moral principles.