Can anyone guide me about the use of Blackheart Hollow? Thanks in advance!

It's quite simple: it restocks VERY rarely and the items are priced in Wizard Tokens like the token shop. If you refresh too much there you will get a temporary ban, so don't do that. My strategy is to have it on my on-site bookmarks and I click on it every now and then, so far I've bought 19 items.

Some people post their restocks here: Post your BHH restocks HERE! V.3 there you will find what item was stocked, how much it costed and the time it showed up. Good luck!!

Thank you so much for the information and guidance <3 Happy New Year!

it stocks one item at a time only, and maybe as much as four times a day but not on any regular schedule?

IMO even if you get shop-banned, in the time you get temporarily banned for the shop might not have anything in it anyways. I wouldn't care too much about it since either you are lucky or you aren't. For instance (if you believe the posters on the thread, and not everyone who restocks at BHH posts there) on 29th November there were several restocks within about twenty minutes, after an eight hour gap.

Thank you <3 Happy New Year!

You are welcome