I don't know, I mean, if you're ready to self-publish, go for it, but the author and I worked together in the past, he trusted me and knew what I was capable at - so he felt I was the better choice. I'm experienced at it, and he's not perhaps - I don't know. Though I know he wanted my maps and deck plans. He didn't tell me otherwise, he just asked if I would. Another would-be author, saw me publishing for other people and struck up a conversation and I made the offer to him.Whats the advantage of using a publishing company like yourself versus LuLu or is that two different things.
Probably because of the deal I make with the author. Lots of publishers hire authors and pay them X cents a word, or a limited time share in profits, or a royalty. When I wasn't an experienced publisher and wanted to develop my Kaidan setting, Steve Russell (RIP) the publisher let me keep the ownership of the setting (in my case), and a split 50:50 in profits - because Kaidan was my baby, and something I wasn't giving up IP or copyright on (so we shared copyright). Now adventure writers usually aren't doing IP work, like my project, but the adventure is their work, so should have some ownership. My deal with them - and I'm not trying to drum up author/designers (my hands are full already), but I split it down middle 50:50 in perpetude and show them the DTRPG monthly sales report to prove it. Since Steve did that for me, I pass it on.
Plus, I'm not just a "known publisher", most people know me for my maps. I've had a long and successful, freelance cartography career. I created the original hand-drawn map of the city of Kasai for The Empty Throne module of the Jade Regent AP (and wrote the city gazetteer, so I have Paizo street cred), almost every map for every AP in the last 6 years published by Legendary Games, are my maps. I've got over 1800 published maps. I even created all the multi-player maps for Call of Duty: Advanced Warfare Strategy Guide. I've done maps for @Morrus for EN5ider and W.O.I.N. So some writers just want my maps for their adventures, and perhaps a reason to come to me... here's a link to my Artstation Gallery, click the images to see entire directories of content. Most publishers don't start as mappers. I did.
Compared to Lulu - it's two different things. Sorry, I'm not trying to brag, rather just answering your question. And I cannot help decide advantage between Lulu and other publishers - I only know my story...