I'm a reviewer (newspaper) who does sometimes review self-published books (local only), and I had an unpleasant interaction with a writer today. (For the record, the author has a small trade publisher.) The interaction brought up a few basic guidelines for soliciting reviews that I'm guessing (and hoping) everyone here already knows extremely well. Nonetheless, maybe there's no harm in restating them.
1. Take no for an answer. If someone acknowledges they don't want to review your book, they may be doing you a favor — i.e., they may know they couldn't give a positive review, and they see no point in writing a harsh critique of a self-published/small-press book. Or the book may not fit their publication's guidelines (that was the case with me today). No amount of arguing about the book's merits will make a difference. Do not cite other critics or personal connections and supposed obligations. Even if they reviewed a past book of yours, they do not have to review this one.
2. Do not send an unsolicited review copy, or allow your publisher to send one, and then demand it back in the absence of a review. Do not offer to pay postage and think that makes it OK. Just please do not do this. We'd prefer that you never ask for a review copy back, but if you must do this, make sure you check before sending that a review is even a possibility.
If you're really reluctant to part with a hardcopy, you could ask the reviewer if he/she will read a PDF or other e-format. The downside to this is that hardcopies hanging around the office provide a physical reminder to read the book. But only if the reviewer was considering reading and reviewing it anyway. (I always have more "acceptable" books than I can review.)
3. If you win an award and attempt to use this as a stick/carrot to get a reluctant reviewer to read your book (which is not a great idea in the first place, see above), be aware that the reviewer will Google the award. In this case, the reviewer discovered that the award had a high entry fee and a long thread in B&BC here.
I can't tell the author this; it would start a longer and even more unpleasant interaction. (The administrators of the award do not respond well to doubts about its legitimacy.) But I think it's worth reminding other writers: Check reputation and credentials before you enter a contest.
Now that I'm done venting — er, reminding — let me just say that I've reviewed self-published books I liked, and others I thought at least had potential. I've interacted with plenty of self-published writers who were polite, professional and just cool people, and who took a "no" gracefully. I think boards like this do a lot to foster that professionalism.