Title: part + model + reference
The title is what Google shows. Instead of "Headlight", write "Right headlight Mercedes W204 2012": part, side, model and year. Include the manufacturer reference when you have it (that's what workshops paste into search).
Unique description, not copied
If the description equals the title, Google has nothing to index. Add compatibilities (valid models and years), real part condition, what's included and shipping and warranty terms. A hundred own words beat a thousand copied from the supplier.
Photos with alt text
First clean photo with the whole part, rest with details and defects if any (builds trust and avoids returns). Fill in the alt text of each photo with the same title formula: that gets you into Google Images too.
Visible stock and price
Show real stock and final price with taxes. "No price, ask" pages neither rank nor convert: the customer goes to competitors.
FAQ
How many photos per page? Between 3 and 5: general, detail, defect if any, reference and packaging.
What if I sell unique scrapyard parts? Even better: each page is a different search opportunity competitors don't have.