I'm guessing by your screen name you're an Aussie, yes? But a more relevant question is, "Are you currently in Australia?" If you're in the U.S. right now, most of us will be able to recommend a number of online and brick-and-mortar places to check out. For example, I often suggest people check out
Guitar Center's used database. Whenever I've spotted something I'm interested in, I call the store, have an associate take a look at the item for a quick physical inspection and if it's within driving distance, I go and check it out for myself.
I've taken a chance a few times on something too far away to inspect, but the only time I ever had to return something was because the neck wouldn't fit on a parts-bass project of mine. Regardless, there's a 30-day return policy. Even if I bring it back to another store, I get my refund, but not the extra $25 I spent on shipping. And given the hassle it would've been to re-box, tag and ship it back to it's store, that's small potatoes.
Now, on to your bass-related question; about the Jaguar, what is the pickup configuration? Better still, is it one of these?
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The only one of these that just didn't do it for me was the "HB" model, but that could either have been a result of a poor/non-existant set-up by the store carrying it or just my personal preference. I haven't had a chance to give the "SS" a proper trial. No one has it near me.
If it was my money, I'd personally lean towards the Fender Jazz, but that's my personal preference. I like the look and feel of the off-set, contoured body. The dimensions of both necks are almost identical, so that's not an issue. That is, unless one is glossy and the other satin-finished along the back of the neck. It can be an issue for some players.
The only thing that concerns me is that they're charging the same price for a used MiM Jazz as the new Jag. I usually only see a Fender Jazz that inexpensive when there's cosmetic finish damage or something's not quite right. If they do maintenance there, I'd ask if they can throw in a set-up for free. If they resist, then ask for it at half-price. If they say, "We already did a set-up", then ask for a full set-up that includes
checking the pots (the potentiometers under the knobs),
pickup height,
truss rod action,
string intonation and
removing any fret buzz. If any of these are out, it can make a bass sound and/or feel unplayable.
Welcome to TalkBass and Happy Hunting, Bill Ford of AU!
EDIT: Oh, and Welcome fellow Late Bloomer! I, too, started later in life. I used to joke that getting myself a bass for my fortieth birthday was the closest thing I'd get to a "mid-life crisis" purchase. Not a sports car or a barely-legal girlfriend (both too much maintenance

), but a Fender Aerodyne instead.