In my neck of the woods almost every auto store will happily test any
alternator you bring. They also test new ones before the sale. I am assuming
that this is true in most places. Had your 'local shop' bothered to use this
free service, they would have either determined that the culprit was not the
alternator or avoided installing a bad one - whichever the case might be.
They should have also tested and recharged your battery, if needed.
Something is telling me that they are either incompetent or taking you for a
ride. Perhaps both...

depending on teh year, i had the smae problem but it turned out to be the
positive battery cable.  i have a 1994 and ford cables on the years 1991 -
1996ish are famous for rotting from the inside out so it may not took bad
but a good charge cant go through.

I would think that if the alternator was not working it would not move up at
all, no matter what.  Did they check your battery?  And as Happy T suggested
check the positive battery cable.  If it is blackened near the terminal (and
even if it's not) it may be rotted away inside.  Is the battery voltage
higher when the engine/alternator is running?

Verify that the FIELD fuse for the alternator is good.  On my '92, this
fuse is at the rear of the main fuse box under the hood on the right
(pass side on US cars) side fender support.  The alternator may be is
self-exciting once the revs are high enough for residual megnetism to
make the initial excitation current.  The excitation may also go
through a dashboard idiot light too.  I'm not at the car or the
manuals, or I'd give a better description.

ALSO:  Please state the year and model of the car you are working on.
My great aunt Claire Voyant died a few years ago, so I can only rely on
what you share in your posts concerning the year and model.  ;)