In posting what follows, I have assumed the OP referred to one's buying the same make and model of camera(s) one previously had but then sold, and not THE same camera, further down the track from having sold this camera, and (buying again) from the original buyer.
With this disclaimer, here goes my story.
Until the mid 1980s, I mostly bought one camera at a time and then sold it to buy another. A Yashica D, then a Rollei (still own it) in the '60s, Nikkormats in the '70s, more Rollei TLRs in the '80s. Then I got stuck into a fulltime career and photography suddenly became something I no longer did, not enough time/too tired/no motivation.
For about 30 years I bought excessively, made little or no use of the gear I bought (in more than one case, I did not even test the gear), held on to it for years but kept it in storage boxes, and then sold, only to buy the same all over again. Eventually this changed to just buy.
Now retired, I've considered this 'situation' at length, and I have decided my obsession with buying cameras came about as the direct result of being in my own full-time consultancy business of my own as a design architect. I disliked many of the projects I successfully bid on and had to complete,especially one office floor I entirely redid four times (for successive state governments) over 15 years including one contract in which I stripped down and again rebuilt the entire office which had never been used and had been left locked up for the entire period. When we were redoing one senior manager's office I found all the original documentation I had given the client at the closing of the previous redesign, in the boxes I had packed for the client, which had not been opened.
So I compensated by buying used camera gear (mostly off Ebay) which I never used but then put away. Psychologically I wonder if I was just replicating my frustrations with the clients by a sort of projection, by indulging in the same behavior in my own life?
After I retired in 2012 I did an extensive stocktake at home and found, among other things, 10 Nikkormat cameras in various degrees of usability, each with a 50mm lens, a great assortment of AI and AIS Nikkors, and an entire box of Nikon lens hoods, filters, cases, and assorted brand name gadjets. We won't go into the Hasselblads (one 500C, one 500CM, and THREE ELs, plus lenses, filters, hoods, finders, grips etc etc etc), nor the Rollei TLRs, which have always been my favorite cameras. Suffices to say I could have opened a well stocked secondhand camera shop, had I decided to start a new career in my sixties, but this I wisely resisted.
By then my partner was openly expressed sentiments of concern at my compulsive hoarding, and was delicately pressuring me to bite the bullet and DO SOMETHING about my camera gear hoarding. Which even I was ready to acknowledge had reached crisis proportions.
So I began downsizing and offloading. Now, almost five years later, I'm down to a reasonable collection of cameras and accessories I plan to use (at least one time) before I pass them on to new owners. All the Hasselblads have gone, also a few of the Nikkormats, almost all my saleable MF cameras, my two Fuji GA645s, and two of the Rolleis.
I shudder to think of the financial loss I incurred from all this impulsive buying. The Nikkormats cost me A$150-$180 each, as I acquired most of them at a time when they were in demand. The same cameras now fetch about $50-$60 on Ebay and with luck, a little more from private sales. Flogging off the 50mm lenses separately has cut my losses a little. A few lenses, like the mint 300 and the never used 80-200 AIS still in its original box with all its papers and even the original sale receipt, will bring in some extra money when I finally decide to part with them. The goal in all this sacrifice, or so I keep reminding myself, is to downsize, not to realise big profits.
It gave me new hope when I learned that modern Nikon D lenses, also E series lenses, can be used on Nikkormats. This means I can use all the D lenses I've accumulated - I won't say any more.
The upside in all this, of course, is the great pleasure I have had over the years in using some of this gear, and the future plans I have to eventually shoot off and process all the B&W and color films in my darkroom fridge and small freezer.
I realise all this may present me as somewhat of an extreme case, but some of it has been a pleasant way to help pass a lifetime, even if now at my age, lugging a 300mm (with a tripod) on a mountain trek in Tamania is more an ordeal than a pleasure.
All this to say, read and be warned. It is an easy trap to fall into, and many of us do.