Don't use Hx tags for body copy. Use the Hx tags as they were intended for headings and subheadings, to create a logical semantic structure for the document.

If you look at your page with CSS turned off, it should come across something like those essay outlines they used to make us do in junior high school.

The headings and subheadings should contain enough keywords to make the topic of the page clear, but keep a light hand about it.

To add to buckworks, from an SEO perspective you would be 'watering down' any potential phrases you target by trying to stuff them into <h1> and <h2> tags... Having descriptive keyword-rich headings give them prominence, relative to the rest of the document.

<p> elements would make the most sense for full sentences. Using <h2> in place of them would look fishy and perhaps garner unwanted attention.

Use H4 for prices and H3 for ID of product
You can extend this to product name (not description) with H1

The general rule for longterm SEO is: use all tags as they are intended by the HTML standard.
<h1>,<h2> are for headings, so use them for headings. <p> is for text paragraphs so use them for text paragraps. A product description could then look for example like this:

<h1>Brand name - product name</h1>
<ul>
<li>Price: 123</li>
<li>Shipping costs: 12</li>
<li>Product Id: 12334</li></ul>
<p>product description</p>

Because search engines assume tags are used as intended by the HTML standard and then weigh the content accordingly. If your <h1> tag contains the brand and product name, the algorithm will assume that this is what your page is about. If you put in the product description, this will not be possible and you have wasted the tag.

Yes, correct, but you can use H4 for your quoted prices to tell SEO benefits...

I use H2 for product name and p tags for the description. Always worked well for me. Using H2 for descriptive sentences repeatedly for each product would I think be counter productive.

Yes, you are right. But imagine that you have one product = one page.

Search engine will notice this.

In that case, I would use either:
H1 for page heading, H2 for product name and <p> for Description.
OR if the Product Name is going to be the Page Main Heading:
H1 for Product Name and <p> for Description.

H tags are SEMANTICALLY "headers". Expanding buckworks' comments, use H tags where the DOCUMENT requires.

This makes sense:

H1 Widget
p text
H2 Widget Use
p text
p price

This does not:

H1 Widget
H2 text
H3 price

In most cases
H1 is the title, and there is only ONE per page
H2 is/are top level sub headings (chapter titles)
H3 are sub-sub headings INSIDE each H2
H4 are sub-sub-sub headings inside each H3
etc...

Avoid using H tags for font styling which is not OUTLINE presentation related.

Avoid using H tags for font styling which is not OUTLINE presentation related.

I did this once or twice in my very early days and couldn't get the pages in question to rank properly until I discovered CSS.

H1: Merchant Name stocks a wide range of Widgets in Townsville
P: Merchant name sells Widgets in it's Townsville Store and online etc. etc.
H2: Big Red Widget with knobs on.
p: W dget detailed description and price ........

WillG... we all have been rude in not welcoming you to Webmasterworld! So... WELCOME!

This is all well and good for the product details page, but what do you all use for index pages? Categories, search results, etc. . . .

Personally I look over the structure and follow the hierarchy, so it depends on "where they fall" in that.

<h1>Widget Category</h1>
<h2>Widget Subcategory</h2>
<h3>Product 1</h3>
<h3>Product 2</h3>
<h3>Product 3</h3>

Sometimes that's an h2 . . .
<h1>Widget Category</h1>
<h2>Product 1</h2>
<h2>Product 2</h2>
<h2>Product 3</h2>

It makes good semantic sense, but in terms of SEO?