well hence why I used the example of midi modules, the going rate for those is usually €100+ at least around here, so I was actually happy I got them for "just" €50 and sometimes even under, of course I'm going to jump on them for that price if I can afford it, which I said I'm lucky I can, because I do know not everyone can just decide to spend even that much. But I'd rather spend €50 than wait for an even better deal and risk going empty handed and instead see the prices rise even higher (which is true for most items).
I personally don't believe that this contributes to rising prices when they often already go for way more when I bought them.
and yes, it took me quite a while to get those deals even, so it wasn't a case of "I wan't it now" it was a combination of always being on the lookout and a good portion of luck on top of it.
staying with the example of the MT-32... I've been looking for one for a while... then one popped up on the local classifieds for €20 or 25 I think, I jumped in excitement... I immediately called up the person and asked if they were willing to ship it to me (cause it was far out of town) but of course multiple people had already declared interest and were willing to pick it up... so I straight up offered €50 because that's what I set as my limit for midi modules and that was what I was willing to spend (they already sold far in excess of €100 on ebay at that time) and I got it... sure, maybe one would have popped up again for €20 some day closer to me, but I wasn't ready to take that chance for an item that is ever increasing in price and had a far higher "value" already.
not trying to justify anything, just explaining my train of thought, but I also don't see how me offering less then the going rate on ebay contributes to rising prices, it's not like that person will suddenly start selling more of them at a higher price :p
...and sure enough, a few months later they started selling for €200+ already and sometimes even for €300.
I saw another one pop up for €50 again this year I think... but I didn't even contact the person, cause I already had one and I wanted someone else to get the chance... though it might have probably gone to a scalper instead, idk ^^
I don't buy things just to resell them, so I usually don't even jump on great deals like that if I have it already, though I do sometimes buy things I fear might end up in scrappers or scalpers hands instead.
90% of my collection comes from scrap lots anyways, so can't really compare prices there.