Canon 300D is the same as the original Digital Rebel.
It's a ten year old, 6MP, 12 bit camera that's still quite capable, so long as it is in good working condition, as the seller claims. $75 is a bargain price. It sold originally for about $1500, body only, if memory serves. Uses the exact same sensor & processor as Canon 10D (that was a little earlier and sold for $1999... as the first DSLR to sell for under $2000 US). I shot these years ago with 10D...
I've made 11x14 prints from both the above images. No problem with the 6MP images from 10D (or 300D/Digital Rebel)... so long as you don't do much cropping.
Batteries are dead simple to find and cheap. It uses BP511/511A. There are generic clones of those available for $5-$6 apiece (compare to around $40-50 apiece for OEM Canon LP-E6 and LP-E8 batteries for similar current models).
Like my 10D, the 300D/Digital Rebel is a bit hard on batteries. One reason for this was the way I have to use my cameras.... Those older models were a little slow to wake up from sleep mode, and I shoot a lot of sports where I need to react very quickly. So I had to set the camera with a long delay before going to sleep, which drains the batteries faster, so I always carried several extras. I also used a battery grip on my 10D, which holds two batteries and gives vertical (portrait orientation) controls.
It also uses easy to find Compact Flash memory cards. Slower 1GB cards are plenty large, but 2GB and 4GB should work fine, too. These smaller sizes are getting harder to find, but still available.
The older Canon Rebel series DSLRs had shutters rated to about 50,000 or 75,000 clicks. So you might want to test a used one with a shutter count software. This figure is just the "mean time to failure", though.... many cameras shoot far more images without problem. Some do less, though, too. It's not a guaranteed number of shots the camera can take before the shutter fails (it's replaceable, but probably not worth it.
The 7-point AF array is pretty simple compared to more current models. But it's adequate.
The Digital Rebel/300D, 10D and earlier (D60 and D30) produce a "CRW" RAW file (Canon cameras now produce a CR2 RAW file). CRW are no longer supported by Canon's own softwares. But there's no problem working them with third party RAW converters such as Adobe Photoshop Elements.
The Craigslist seller is wrong about several things. First, you can shoot RAW (CRW) in Av, Tv, P, M and B exposure modes. Three of those (Av, Tv, P) are auto exposure modes. It's only when you get into the pre-programmed "scene modes" (such as "running man"/sports, "mountain"/scenic, etc.) that you are limited to JPEGs only.
All in all, if that Digital Rebel is in good working condition, it's a fine old camera. (Note: it won't shoot RAW + JPEG... both at the same time... the way newer models can. The 10D can't do RAW + JPEG, either.)
It cannot shoot video and doesn't have a Live View mode. The LCD monitor on the back is rather small (under 2" diag., if I recall).
I have a 300D/Digital Rebel that's not working, I bought for a few $ to try to repair, but is beyond help (it shorted out when someone jammed a memory card in and bent the pins in the socket)... SO it's going to be used for a Canon Loyalty purchase instead.
I don't see anywhere in the ad that Craigslist seller is claiming he bought it new 3 years ago.... It's definitely a ten year old model (and the Rebel series has been expanded and refreshed almost yearly, so there have been a lot of models since then).
EDIT: Okay, I read more of the posts and see now that you talked with the seller and that over the phone he claimed to have bought it new three years ago... Yes, that is a little suspicious. I would imagine there were no new 300D/Digital Rebels available beyond 2005/2006 at the latest. So either he's having a memory lapse or exaggerating. But it's also clear to me from reading the ad on CL that he's not very knowledgeable about the camera (as noted above).
The 300D/Digital Rebel was the very first Canon to be able to use EF-S lenses that are especially designed for the smaller APS-C sensor format cameras. All subsequent APS-C models can accommodate all these lenses (however 10D and earlier cannot). This gives you access to some excellent, high quality EF-S lenses, such as the EF-S 10-22mm, EF-S 10-18mm IS, EF-S 17-55/2.8 IS, EF-S 15-85mm IS and EF-S 60/2.8 Macro. In fact, 300D/Digital Rebel and all later APS-C models can use
all EF and EF-S lenses Canon makes. (Full frame models such as 6D and 5D series can only use EF lenses.)
300D/Digital Rebel is a little plasticky. The more expensive 10D has a magnesium body shell and uses a true pentaprism, while the 300D uses a penta-mirror to reduce cost and weight. The 10D also uses a BG-ED3 battery grip, one of the best Canon has made, which also fit the D60 and D30. 300D probably has an available battery grip, too... though I'm not familiar with it.
Otherwise, 300D and 10D are essentially the same camera.
The EF-S 18-55mm lens on that 300D/Digital Rebel is probably the original version that was sold with it and that's not all that great, though might be usable for the time being. It's been revised several times, but is easy to update to a newer lens, if you wish. A later 18-55 IS or 18-55 IS STM would be a much better lens that's still rather inexpensive. Personally I used an EF 28-135mm IS a lot and find it's optically excellent and a very nice walk-around lens, fast focusing, close focusing, with helpful image stabilization (even if it's not particularly wide on a crop camera... I paired it up with a Tokina 12-24/4 that
will work on a 10D, as will all third party "crop only" lenses). 28-135 can be picked up used for $200-250. Tokina 12-24 can be found for around $350-400). Above images were made with a Canon EF 50/1.4 lens.
If you decide to take a closer look at the 300D/Digital Rebel, download and study the manual so you know how it works and can test it before buying. Or, even better yet, if you have a friend who uses Canon DSLRs and is familiar with them, invite him or her along and have them look at the camera with you.
$75 isn't a lot to risk on a DSLR, at any rate.
If you have more to spend and want a new camera instead of a used one... I'd suggest looking at Canon T3i and T5i. The latter has an articulated LCD screen and a few other improvement, but both are excellent, 18MP models capable of very high quality images.
I'm sure some of the Nikon cameras mentioned would serve just as well. To decide between them, I'd suggest you go to a store and handle some Nikon and Canon models... maybe some Pentax, Sony, Oly etc., too... to see what feels most comfortable to you. They all are capable and can meet most people's needs. So it's really more a matter of which feels most comfortable and easy to use.