I thought I would post up some of the things I do to finish these 3D printed items. Namely gluing and Finishing.
Gluing multiple parts. If the item is printed in ABS, the best glue is an acetone / plastic welding cement: Most plastic cements work, eg the type for airfix kits. ABS glue and if you can find it in hardware stores, PVC plumbers glue, sometimes is a blue color. You can also try acetone (nail polish remover)
Finishing:
Once you glue the parts you may need to sand the visible lines where the parts have been glued. Use your judgement but I just use a power mouse sanded and then by hand.
Another trick is to liberally paint the blaster in acetone, this will soften the print lines.
And yet another is to use "hammered" finish metal spray paint as the undercoat. Its a really thick paint that tends to fill in the print lines, though it takes a day to dry. I usually use the silver, this way if the item gets scratched it looks like metal.
The blaster below was a "second" as it didnt print very well and hence It wasnt up to scratch to pass on to others paying for the printing service. I was able to more or less rescue it using the above techniques. You can see how the hammered metal spray seems to fill most of the print lines. another sand and its ready for proper painting.