Blockquote tags are for actual long passages of quoted material, and should be used in these cases.

Automated tests cannot tell if text is an actual quote or not, so the content of any blockquote should be reviwed manually.

Example

Wrong

<p>A long quote of several sentences. This should probably be placed in a blockquote, as it is too long to read in a single sentence, and the presence of a blockquote tag would help indicate it is actually an excerpt from somewhere else.</p>

Right

<p><blockquote>A long quote of several sentences. This should probably be placed in a blockquote, as it is too long to read in a single sentence, and the presence of a blockquote tag would help indicate it is actually an excerpt from somewhere else.</blockquote>