Buying used is the best way to get more bass for your money, and most used basses are in great shape. A few minutes of checking keeps you away from the ones that aren't.
What to look for
Ask for the photos you need: the whole neck from the side, the frets, the back of the neck, the electronics cavity and the serial number.
Check the neck. It should be close to straight, and the seller should confirm the truss rod still adjusts.
Listen to the electronics. Every pickup and knob should work without crackling, and the output jack shouldn't cut out when the cable moves.
Look at fret wear. Grooves under the strings on the first few frets mean a fret level or replacement may be coming.
Use the marketplace's checkout. Paying through Reverb or eBay keeps their buyer protection. Be wary of anyone asking for payment outside the site.
Compare prices. Check what the same model sells for elsewhere on this site before you make an offer.