If you can't answer them within a reasonable time frame (and 3+ days is not reasonable, imo), you should either delegate or hire someone to handle this stuff for you. But, hey, they're just customers. Their time doesn't really matter.

If I have a question about a product, I'll make an inquiry. If I don't get a response within a day or so, I'll get what i need from someone else and scratch the first company off my list. I have zero tolerance for poor customer service.

The internet has forever changed the way people shop. Unless you're selling one-of-a-kind, hand-built items, your products are available somewhere else. If you're also running a brick and mortar store, those same products are most likely available somewhere else for far cheaper. The simple reality is this: If you can't beat those vendors with superior customer service, there's no reason for buyers to give you their money.

None.