They told me that commercial/industrial rates were higher than residential, so they're either lying or insane. They also said they won't give an industrial rate to a residence.
But what if you do your business in residential area? In large European cities many small businesses are located in multistory buildings where people also live, just occupying one of the apartments (usually on first floor).
I don't know what electric prices they pay, but I think industrial because our supplier offer only two variants: "household" and "business".
BTW, professional miners could consume a lot of power which is more than grid's capacity for apartments, so upgrading to industrial consumer and extra cabling is inevitable.
Industrial prices are not always cheaper.
It has a lot to do with your location and what the local power supply comes from. The cheapest places in the country for electricity usually get it from hydroelectric. In these areas, because there are huge surpluses of energy, what will happen is that they will offer it cheaper to large businesses or sometimes business parks will even be created to house multiple new businesses.