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First UGC should be published after verification and approval of moderator. So you may need to change the process of publishing content on the page.

Incase of 302 or 307 your original page will still remain in cache and you may get duplication content penalty.

If you already know which pages have copy right issues then you remove the content. mark the pages as no-index, follow. Make them index follow as soon as you have original piece of content written on them.

If your product is temporarily unavailable then don't redirect. display a message on the same page that "product is temporarily unavailable". You may also display some relevant product and categories but don't redirect.