Do I charge general excise tax on sales or service to a 501c3 in Hawaii?

Other answer:

Howard M:
if they don't have an exempt certificate from the taxing agency in Hawaii, yes, you charge them sales tax
a non profit is not exempt from paying sales tax unless they have an exemption
Dan B:
Yes, unless they have a tax exempt form on file with you. If this organization is using the purchases in-house (not intended for resale), then the items purchases is taxable. Sales tax exemption applies only to items intended for resale. When sold, they'd collect the sales tax from the purchaser and forward it to the state.
Bostonian In MO:
Passing GET on to your customers is optional if the customer agrees to have it separately stated. The tax is on the business, not the customer, so virtually all sales are taxable except the sale of goods to the federal government or credit unions.