Hi, I have hundreds of items that are very similars and there’s only so much keywords I can use for each pages or items to avoid duplicated contents. Should I put the reminding pages in the noindex to avoid duplicated contents.
Also, I have lots of permanently sold out items, should I use 301 redirect, noindex tag, 410 or just delete it to have the lease effect on my SEO.
It’s not necessarily bad to have lots of similar products as long as you have unique, descriptive titles, h1s, and body descriptions. A common example is manufacturer part websites. They make sure to have the SKU or part ID in the title, h1, and body and Google is able to route queries accordingly.
For targeting generic queries, build collections to group similar products since the products themselves are too overly similar for search engines to make sense of which to rank for generic queries (e.g. “drywall screws” is a good collection query and “#6 1.25 inch #2 phillips drywall screw” is a good product page query so you’d want to make sure the product page has all that info in the title, h1, and description.
Re: what to do with OOS products, this is a helpful article that walks you through that decision making process (it depends): https://ahrefs.com/blog/ecommerce-out-of-stock-products/