No, 10% isn't "average" or "standard." And I'm not just saying that because all commissions are negotiable. Where I am, the commission tends to be less. It also depends, as noted, on whether it includes the land. What it comes down to is that there's still a lot of work involved in selling a mobile or manufactured home. And a 6% commission (just a hypothetical number) on a $30,000 transaction, perhaps split 4 ways (listing agent, buyer's agent, broker of the listing agent, broker of the buyer's agent) results in almost no commission. That's $450. So, I agree you'll often see commission percentages higher on mobile homes than on stick-built on their own land. And those higher commissions can certainly be justified. But: No standard.
And I agree with Tony that the commission shouldn't be at the top of your list of questions. It IS a specialized service, and you want someone who knows what they're doing.
Hope that helps.