When I ran a busines with RL inventory, I used to get asked for donations all the time. And I was a very very small business. Many of the requests were quite ridiculous. Some came on a regular monthly basis.
In Second Life, donations are a bit different. After all, if I give out a few free wings at an event, I am not out any money. (Unlike a RL business where I'd be out whatever wholesale amount I paid for that item.) Still, I get a lot of requests for stuff that would cost me time and money. Advertising is one of the most difficult ones. I really don't have any need for advertising beyond this blog, forums, and classified ads. If I made more clothes, an ad in one of the fashionista mags or blogs would make sense too, I think. But other than that, I really really have to be sold on an advertising pitch and NO ONE has been able to do that yet.
Half the problem is that people don't think outside of the box and they are still trying to do advertising in the same way that it works in RL. I suspect the first person who does this will make a windfall, but they will really need an idea that slams it out of the ball park.
In addition to advertising, there are those people who have the balls to ask for wings to resell, scripts to resell, full perm scripts, full perm textures, and anything else that involves them doing no work at the expense of my own time and effort. Of course, these people are easy to say no to . . . but still, you get enough of these requests and you start wanting to shout "TAKE BOTH OF MY KIDNEYS WHILE YOU ARE AT IT."
And then there are the people who want vendor space or something like that. I respect these people for having initiative, at least they are trying to make stuff on their own. But I can't say yes to everyone.
So . . . I think when SL clothes designers or other sellers get a little snippy about giving out preview items to bloggers, this is why. The reason is less the bloggers and more the people before who want a free ride and both kidneys while they sit on the couch. It's not professional to get to that boiling point, but after a while, these request for your hardwork by slackers is just tiring.
And just to be clear, Material Squirrel doesn't have a policy on preview items for bloggers. If I were asked, I'd want to see your blog. And I'd probably say yes. Can't say that I've ever been asked tho.