I did as you taught.
Here's a screenshot.
www.awesomescreenshot.com/image/61701/7b...bd73ac9103b369fe8a02

Then I cleared the cache joomla and joomsef
www.awesomescreenshot.com/image/61723/90...8aa663193a6dab9db7cf

URL were quite bad.
site.com/list-all-products.html?virtuemart_manufacturer_id=2 ----> URL very bad

URL should be such
site.com/manufacturer.html -----> good URL

Is there a reason why you need .html in the url? in fact the trend is more like urls domain.com/manufacturer

you can always go to Sef URL management, click NEW, enter the old non-sef url and enter new url in the sef line to create whatever url you want

Thank you for your advice.
I bought this VirtueMart JoomSEF Extension to have it done the job.
I need to create yourself a good URL and tags?
Why does VirtueMart JoomSEF Extension tags for manufacturers?
Programmers developer has not made a lot of work to bring VirtueMart JoomSEF Extension to perfection.
But programmers do not want to finish his work.
I am very saddened.

I think you should submit the support ticket, and they check it on your web directly, It definitely creates the urls.