Internet reigns supreme. Most of what I purchase, I get from Ebay or IDJNOW.
I did buy my Alto TS215 speakers from Guitar Center. I also bought 1 of my Alto TS110As there a few years ago, then got the 2nd one from IDJNOW. Again, I don't know how much mark up there is for the store on lower priced DJ Speakers. They probably only make like 30 - 35%%, and when they run a 15% OFF sale, that cuts their profits down pretty good. When they have to price march a competitor even lower, the profits are real small.
Then, some of products they sell are simply over priced. Much of their lighting is at regular MAP sale prices, and are usually excluded from their promotions. I can go online and always find lower prices with free shipping on DJ lighting effects.
Speaker Cables, Microphones, MIC cables, and other accessories are all higher priced than what I can get them for online. They don't really sell cases, or carry bags there for the stuff they do sell which I always thought was a big mistake...Missed sale opportunities there.
I think last time I was in GC, I bought a fresh roll of Gaffers Tape because they sell a large roll for $19.95...which is comparable to what I can order it for off of Ebay. I think I also bought another C Clamp there which costs like $7.95 or $8.95...with shipping about the same off of Ebay.
Really, Guitar Center is a place I go if I need something for a gig that is coming up, and not enough time to order it online these days. I use to buy lighting there, and did buy some speakers there in the past, but today, I wouldn't purchase that stuff there because better deals are to be had on Ebay or Amazon etc.