As far as style is concerned:

1) try to use "for := range" loops instead of the traditional for

2) "var result [4]string" - really seems like this wants to be a struct with a couple of fields.

  type result struct {
    id    string
    name  string
    brand string
    price string
  }

  result.id = product
  result.name = e.ChildText("h3 a")
  result.brand = " "
  result.price = e.ChildText("span.value")

3b) The "visitStore" method does a switch on "store", but it is in a hot loop. This is a good candidate for micro-optimisation-is-the-root-of-all-evil debates later down the road. It's better to avoid those, and there's a number of simple solutions here to prevent that "constant check" in the hot loop.

4) Using defer in for loops is always a red flag. While it is technically correct, it's very likely not what you want here. Imagine that you have 10k products to visit, for 10 stores. The file for the first store will be flushed and closed only after your main function exists (your entire program in this case). What you would want is to open a file, visit all products, flush the writes and close the file handle, and only then move on to the next store. In other words, the lines 76-98 (the body of your main for loop) should be a separate function so your "defer"s happen when a loop iteration terminates, and not when the "main" function exists.

as an idea I'd suggest to evaluate your codebase with the multiple llms available now using the free tier (deepseek V3, llama 3.3 versatile on groq, gemini-exp-.. on google ai studio and so on)

on each llm provider you can find prompting best practices or techniques to improve your eval prompt and eval your code correctly

at least the feedback loop would be faster

if you already thought about it or already did that, well ... great