SEO-wise its neutral, per Amazon's and eBay's affiliate T+Cs it's not only black hat but they will suspend your payment and prosecute you for cookie stuffing. Of course the affiliate managers never do that because RetailMeNot is a juggernaut of mostly legitimate traffic, cheating only a little. Try utilizing these tactics as a small blog and you will be banned from their programs for life. Bullshit double standard.