Trademarks are not global, but for individual markets. For example, a company I worked for employed an "Apple Security" company to provide security guards - nothing that Apple Inc. could do about it because they are in totally different markets.
You would need to check in which markets UGG is a registered trademark. Unless Deckers Outdoor Corporation sells or repairs musical instruments, you should be able to get a registered trademark in that market. The "130 countries" is only relevant if you want to trade in these countries yourself.
PS. When you look at the trademarks that this "Deckers Outdoor Corporation" owns, in the countries that you are interested in, you should find that each trademark is assigned to a market. For example Google tells me that one of their "UGG" trademarks is registered for "Leather And Imitations Of Leather, And Goods Made Of These Materials And Not Included In Other Classes; Animal Skins, Hides; Trunks And Traveling Bags; Umbrellas, Parasols And Walking Sticks; Whips, Harness And Saddlery". If you make any of those, you lose. Used Guitars don't seem to fall into any of those categories (but they have more than one UGG trademark, and I'd avoid making leather or imitation leather cases for your guitars).
Of course you shouldn't trust Google but go to an official source.
PS. I hadn't realised that this company has a highly successful product that is much more famous than the company, and that gets copied a lot, and therefore they are likely willing to litigate quickly and have experience doing it. Being sued is trouble and costs time and money even if you are legally in the right.