Singles, how do you prevent awkwardness when someone assumes you're not single?

I can't be the only one who has those moments.

I was registering for a DIY-type class today and the conversation went like this:
Woman: "It's free to bring your husband. Would you like to sign him up?"
Me: "I'm not married."
Her: Pauses awkwardly "Oh, well, you can bring your boyfriend or significant other."
Me: "I don't have one of those either."
Her: Pauses twice as long."Oh, that's ok dear. (reassuringly) You can bring a friend instead. Most people bring spouses, but that isn't a rule."
Me: No, it'll just be me. I don't have anyone I'd like to bring.
Her: "Oh, well, um... How about a coworker then? You could bring someone you work with. Maybe even split the cost."
Me: I work from home and I work alone. I have no coworkers. Please just sign me up alone.
Dead silence.

Perhaps the worst was maybe a week or so after my ex husband moved out. I bought a bunk bed for one of my kids from Craig's List and went to pick it up.
Woman: "I'm sorry. My husband is running out to a meeting and can't disassemble the bed. Can your husband come by and do it?"
Me: "It's fine. I can do it."
Woman: "I think it would be easier if you had your husband do it."
Me: "I'm divorcing and unattached, but I'm sure I can handle it." Holds up tool box.
Her: "Oh, I'm so sorry." Places arm around me. 

Or, the guy who sold me my new air conditioner and suggested I have my husband look over the specs before I chose one. -_- Or, the flooring place that wouldn't come give me an estimate unless I assured them I was the sole decision-maker. They asked 20 different ways who else might be involved in decisions or might be affected by my choice. Bah.