If you are referring to the download page with “Client Download” and “Mirror Download” there is none, just pick one. A mirror download is supposed to be same files but hosted somewhere else, it’s just to reduce bandwidth costs usually or split the charge.
The myth that “marketplace bots” are the ones taking your items before you are able to buy them off the marketplace is incorrect.
I understand your frustration about RNG, she is a cruel mistress after all, but the reason as to why you are sometimes not able to get items from the marketplace depend on several things.
Latency plays a big part in buying things from the marketplace, if you and another person clicks “Buy” at the same time, the person with the lowest latency will more often than not be the person to get the item.
However, RNG also plays a big factor in buying things from the marketplace, as weird as it may sound. That’s simply how Black Desert Online works.
More ways to acquire boss gear will soon be available, from options such as Night Vendor etc.
However I will look over the current drop rates for Muskan’s Boots and see if I notice anything out of the ordinary.
Also send screenshot of ur name so we can better tell whats the problem
As @Czepixter says, could you list the names you have attempted to use?
Possibly the name is already in use and thus preventing you from using it, even though the error message may say otherwise.