There is a difference in some cases, but not all cases.
Often, while I tally cost and supply advice, customers become sold on the fact that I know what I'm talking about, and that makes a sale.
Sometimes, they just want a price, and that is estimating.
So the two can be distinctly different, except in the cases when they are not separate; possibly occuring simultaneously in the same session.
Sometimes, I include something I notice that I was not called out for, and I suspect other estimators would not have included it since it was not the concern. And I purposely mention the need and include it in an estimate which I know is a better deal that other estimates. And the other companies have come and gone. Its a version of estimating, that I know will make a sale in 90% of the cases when I can do it.
Sales and Estimating are always separate for the less experienced, or individuals who lack the ability to combine the two. Its within the top tier of industry professionals where the ability and training resides to make estimating and sales blend together when the opportunity arises.