It's been awhile since the thread was active so I hope I remember it correctly; what I can remember is that there is no need for disclosure (by ASA guidelines) unless money is exchanged and the brand has creative input into the content, it is then marked as a sponsored post or #AD.
So for example if brand A pays blogger B for guaranteed space on their blog/instagram/etc. for an agreed fee based on following and traffic to platform of choice but has no input as to how Blogger B showcases or what is showcased there is no requirement to disclose anything. The brand can still demand non-creative things like when it is scheduled, type of post, etc. just no input anything 'creative'. Which makes it all rather dodgy as the only parties privy to those contracts are the blogger and the brand/agencies involved so how this is all monitored remains a bit of a mystery to me and seems highly susceptible for fraudulent activity.
There is no requirement to individually disclose affiliate linking either. This means that if you click the link to the product it usually has a cookie attached for 30-90 days (some even longer) and if you end up buying through the affiliate link the blogger will get a percentage of your total sale purchase (speculated to be anything from under 5% up to 10% and varies per e-tailer).
There is no necessity to disclose or register (for tax purposes) gifted items from brands either, they are considered press samples and are usually sent unsolicited to bloggers.
Suffice to say, I no longer subscribe to many blogs (sum total of 1 at the moment). It's all too murky for me to consistently feel out who is trustworthy or not, so I simply don't bother.
Saying all that, Mango is part of the Inditex group (Zara among others) which is notorious for spending the least amount of money on advertising, if any. So unless they have recently changed strategies it's unlikely to be stealth advertising. There will likely be affiliate linking involved as that pretty much drives the entire e-tail market, so it might just be this blogger's strategy of showcasing a lot of lower priced items as that will generate more volume sales on a possibly high earning affiliate percentage for that particular e-store in comparison to other e-tailers.