That's my understanding

I think people are overestimating the amount of cyberware the average shadowrun individual has. I would imagine that the vast majority are limited to datajacks, maybe some nanotats and cosmetic bioware. Sure, you can get a cyberlimb but it's cheaper just to get some flavor of synthetic muscle than get a stronger/better cyberarm and even in the gritty future the number of individuals missing limbs should be pretty minimal. I would imagine that the vast, vast majority of people are burried with the fairly minimal cyberware they had in their life, since no one really wants a used datajack. I just can't see enough combat type cyberware, like wired reflexes, out there that there's a consistent process; if you can sell it to a shady vendor or for scrap or something you might but it's pretty hard to move. Even the corps probably don't use all of it, after all you don't want your elite units using used stuff so some of the stuff might get passed down to standard security but carving people up afterwards probably has some bad effects on morale. For example, I can't see Renraku carving up their super-honor Red Samurai after death just so a security guard gets a used Wired Reflexes 2 which probably won't make much of a difference to him. I would imagine a lot of cyberware gets buried.

Interesting idea for a low level run, go grave robbing for cyberware.

Also that "second hand cyberware" is likely to be outdated, sometimes severely, which means it won't sell unless you drop the price and quickly make the whole "collecting bits from dead peoples" far from lucrative.

Ther's probably still a market, but in my opnion it's more likely a grey one - vending the recycled oldies to peoples who can't afford or have no legal acces to new hardware.

Peoples like gangers, some third world presidente or generalissimo's pretorian guard and the like.

Another point ot consider too : second hand cyberawre is likely to be an horrible mix-and-mash of types and even brands. Say you want ten units of second-hand wired reflexes II - you'll probably get ten different system, with a range of two if not three generations of conception by at least four different producers.
Which would make it about useless for anyone buying in any sort of numbers. The cost of maintaining that sort of disparate mix of equipment will quickly eat through any initial saving.

I´m with you on that interpretation.

Regeneration is by definition going to reject anything that doesn't fit within the natural body. Boneplating would be pushed out as the bone regrows. - Tailored genes would probably trick it though.

Bioware muscles, if not high enough quality, the body would begin growing the original muscles, slowly expelling the bio.