yes it is usually the grounds that go bad, our electricians love to replace parts, perfectly good parts.
to test the alternator, you need to connect a voltmeter to battery terminals.
it should be 14 +. even if lights and ac are on. if it drops, pull the throttle to increase rpm, if it increases back to normal, good, if not, check the grounding.
for diagnosis, add a wire straight to alternator body from battery negative.
to check charging wire, one probe of voltmeter on alternator positive terminal (it is the one where charging wire is bolted on). and the other probe on battery negative. if it shows more voltage this way, compared to both probes at battery terminal, then there is a bad connection somewhere.
you only need to buy a multimeter that costs max 1000 rs