Oh, and...when I pull the thread out of the machine at the end of a seam, in order to cut it off, I really have to pull hard, and I can feel and hear the thread straining.

It's too tight. The service guy did it by the numbers, not by the way it feels.

Google "how to adjust bobbin tension" and get the bobbin set right, then adjust the upper to get good stitching.

I really just want to take it back. I don't want to deal with trying to set the bobbin tension; it's too hard. I don't really trust myself to get it right. I mean, I paid $80, and I expected it to be right. Maybe I'll walk it over on Saturday and get the store owner to look at it.

Oh, I found a link to a paper by the University of Kentucky Cooperative Extension Service on sewing-machine tension that gave info on how to tell if the WHOLE THING is too tight! (everybody else just gives info on how to tell if they're out of balance).

You fold a rectangle of fabric in half (to get two layers), and stitch across it on the bias.

Then you hold the stitching line between thumb and finger at each end and pull hard along the bias (so the fabric stretches), strongly enough to break threads.

Here's the link.

http://www2.ca.uky.edu/hes/fcs/FACTSHTS/CT-MMB-213.pdf

One
of four things will happen:
1. The upper thread only may break. This shows that the upper tension is tighter
than the lower.
2. The lower thread only may-break. This shows that the upper tension is looser
than the lower.
3. Both threads may break. This shows that the tensions are balanced. The
stitch may be perfect. However, if the cloth puckers at the same time, both
tensions may be too tight.
4. Neither thread may break. This shows that tensions are balanced but both
may be too loose.

I'm going to try this tonight.

And here's another detailed guide to how to tell if the bobbin tension itself (again, not whether it's balanced) is too tight:

http://www.singersewinginfo.co.uk/tension/

you can tie a weight of the correct amount [30 to 40g. (1-1/4 to 1-1/2 oz)] onto the thread and then jerk the bobbin gently upwards. This should cause 2 to 5 cm (1" to 2") of thread to slide through, but not for it to unwind freely.

If you don't have a set of small weights, then you can use digital scales to weigh sugar, sand etc into a small ziplock bag to use instead.

Well, an update: I did the weight test above, and it dropped 1 to 2 inches, so that looked right.

Then I took the machine back to the shop (Yikes! I discovered that I'd called them about 2 hours before they were closing for good!). The guy who runs the shop looked at it and said that this tight tension is actually the way it's supposed to be.

So, there you go! it's fine at this tight setting, and I've had my tension too loose all my life.

Good thing you called them when you did.

The general advice is to set top tension some where between 4 and 5 (assuming the dial is numbered 0-9), then test sew two layers of light weight cotton (shirt / quilting type fabric) using regular "sew it all thread". Don't use anyting like Gütermann's top stitch thread or extra strength, it's way too thick for adjusting tension :- )