Dont panic chris.. you've done all the right things, made contact and maintained it, shipped the goods promptly etc..

I usually send an invoice straight after the item ends, then wait 7 days before emailing them again, but most pay promptly, expecially if they are using paypal.

I always e mail someone to let them know funds have cleared and again when I post the item along with any tracking numbers.

In general I just treat others as I would wish to be treated myself, I have always found that philosophy pays dividends in all walks of life.

I use the sigma your considering more than any other lens at present and cant fault it for the money.

I've had the same problem.
I use manual focus to set mine on infinity for widefield astro shots but keep getting soft images, even at the wide end of the scale.
I've now just bought a sigma f2.8 28mm manual focus (PKA) to do the job and given up with the kit zoom.
I'm also looking at replacing the kit zoom with something like the sigma 24-135 f2.8/4 if I can find one, I know that lens has some issues but I think it'll do a better job all round.

Theres a great plug in for photoshop users avilable free called de noise.
I use it for astro photo's and find it works really well on all images.
Its also worth looking at crispimage from the same company as I have found it the best and easiest to use sharpening tool available

http://www.softwhile.com/product_dn.html