Hot Toys products, (i believe i already said it) i get a 10-25% discount on figures. The discount range depends on how expensive the figure itself is. Sideshow has oftentimes given me products of their making, to which i usually will mention that i got it given to me. Hot Toys, i don't think they can just give those figures away as much because they aren't their product. I don't know that for certain. I do know that some reviewers get them for free. I don't make a stink out of it because as i explained, i like paying for my figures because it allows me to maintain my honesty in my reviews. Paying also allows me to write things off come tax time. When it comes to Boba Fett, i paid a 10% discounted price. I also don't pay for shipping because i'm only an hour away from Sideshow.
Sideshow has suggested i review many tings in the several years i've worked with them. I turn many things down because i have no interest in the item. By that i mean, i don't know anything about the property. For example, their Tychus figure from Starcraft. It was offered to me (yes for free) and i turned it down. I want to say it ultimately went to Sean Long instead. I didn't want to review it because i don't know anything about the Starcraft franchise. Same with Hot Toys iteams, there are some franchises i know nothing about. My "system" is when a new figure comes out, i contact the people at Sideshow and they put it on a preorder list for me. These are usually figures i am personally interested in. We work out whatever discount is appropriate (for Hot Toys items) and i do the monthly payments on them. Occasionally things come out and they message me saying "hey, you don't have this on your preorder list, but would you want to review it?" I consider what the item is and if i think a review will perform well, i'll buy the figure (again with my discount). Ultimately, most of those figures i sell because they don't fit in my overall collection.
This is my situation and i cannot speak to what others have in place. You're welcome to ask those people, it's different for all of us.