I buy most of my kitties at Auction unless I'm looking for something in particular and then I'll do the leg work and go secondary market hopping. Selling at Auctions lately has been on the slow side. Some breeders/sellers have dropped the start bids on their kitties to get a sale, sometimes asking a lot less than they are worth. Though good for buyers, maybe not so good for the seller. Bargains are available at Auctions, I think even more so nowadays with the secondary market being the way it is, a lot more breeders have come to rely on Auctions for kitty sales.
Bid boards can also be a good source of kitty bargains. The only issues with the bid boards are ...... lag monsters which can cause bid boards to take 15 minutes plus to fully rez, by that time, people are usually bored and moved on. Also the turn around on the board themselves. Sometimes bid boards are left far too long after their rentals have expired, to be restarted for the next user.
As for Marketplace ........ I once tried to get kitties to the Marketplace as I already have a store on there ....... was a no go. There are no clear instructions on how to get the kitties up there and I wasn't going to risk losing kitties.
Group notices are a great way to advertise your store, Auction or Kitties ......... BUT ........ you get those who really do take the p**s when it comes to spamming, sending out the exact same message in various groups, EVERY HOUR !!!! Worst part is, it's their group and yet they tell group members not to spam yet they do it themselves. It shouldn't be do as I say, not as I do. Lead by example.
As for advertising on websites, unless the link is posted in a notice, I'm not likely to see them. Some people don't have the time to be searching site after site looking for something unless it's advertised. Also make sure your web page is from a recognisable, easily identified web provider like flickr as most people don't like clicking links due to all the scams out there.
A good tool for advertising all your web pages, stores in one go is notecard it. These can be attached to notices and there isn't much you con't attach to notecards, like LM's, web links, textures. It's about getting all the info out there in a short and snappy burst without making people have to read and read. Also how you word notices, even decorate them makes a difference. Make it stand out, make it grab people and you stand a better chance of people taking a look. Just make sure you don't go OTT on the decor and forget the info.
Last but not least. Store Decor. I love a store where people have taken the time and imagination to actually decorate it. I know most will say it's a waste of prims but those few prims could again grab people's attentions and draw them in. As some know, I LOVE to decorate my stores and they are never the same for too long and I try to decorate it in the seasons we are in (currently winter/christmas). I do this partly to attract people and partly because I just have a strange need to decorate my stores LOL, being a builder helps. There are so many low prim, low price items out there to decorate your stores with. Just think of a theme your comfortable with and doesn't violate any sim rules and go for it.
Well that's my pennies worth, hope it helps someone

RED