I think, bernardswatch, if influencers are guided by the principle of never deceiving their audience about advertising, then it's actually all quite straight forward.
If they were given a handbag to feature twice on Instagram, it still remains a gift after those two features and should be tagged as such.
An influencer might be able to strategically feature a bottle of shampoo in their bathroom shelfie, but if it was sent to them as a gift it should be tagged as such.
I don't think the average consumer understands the word 'sample' to mean free product, whereas #gift or the awful #gifted is understood by everyone.
I personally think all products being promoted should be tagged with #AD because it IS advertising. I have never seen a bad review of a free product so it must be... advertising. However, I appreciate the ASA guidelines stipulate #AD only needs to be used when the brand has editorial control.
If being guided by the mantra of 'I must not deceive my followers in regards to advertising' is too tricky to implement, the ASA really needs to standardise the types of agreements brands and influencers can make - I would have thought influencers would prefer fewer guidelines in return for clear transparency.
And don't get me started on affiliate links - if you are savvy enough to sign up to an affiliate program and create an affiliate link, you are capable of typing A F F I L I A T E L I N K.