Generally speaking, popular espresso machines with good reliability track records go for as much as 70% current retail, but most are 50% or less.
Isomac was once the darling of the espresso internet, but has since been displaced by Quickmill, Vibiemme, Expobar, etc. Fortunately for current owners, 1st-line has revived the line with the
Isomac Tea II, so potential buyers will be comforted that they're not buying a boat anchor. In all fairness, Isomac uses many standard components, so 1st-line's support notwithstanding, it shouldn't be difficult to obtain repair parts for years to come. With the caveat that I am not an eBay watcher, I would expect an older Isomac to sell below average as used espresso equipment goes.
I am not familiar with the BZ99, but judging from the online photos, it's in the same class as the Livia 90 widely sold in the US. Assuming it's in good condition, it probably will be middle of the pack price-wise, assuming of course it's in very good condition. If the machine has been poorly maintained or has evidence of scale buildup, the cost will drop dramatically (e.g., 30% retail if you're lucky).
PS: Please note that
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