One of my clients has an online store that sells t-shirts. Originally his SEO rankings improved steadily over a course of a few months as his products remained stable. Unfortunately after he sold a lot of his t-shirts and made new ones - he removed a lot of those links/products which really hurt the site's SEO, but he has new products/links now...but I'm sure it'll keep cycling through the year.

Any authority or backlinks he's built from those products he's removed is now wasted SEO effort. Currently there is no blog and the only content are descriptions of the products. Plus another issue is the business is seasonal, so typically in the colder winter months, the store doesn't do well.

What's the easiest and most reliable way for a t-shirt store to improve their SEO without relying on the products? Is starting a blog a horrible idea?