One of the absolute easiest things you can do in post-production to improve the quality of your photography is to do keystone correction, which is sometimes referred to as straightening verticals.

Below is a before & after example. I've purposefully selected a decent starting image to illustrate the point that even a really nice photo significantly benefits from this technique.

If you've ever seen serious architectural photography, you've probably noticed how perfectly straight all of the vertical and horizontal lines are. The way this is achieved is through a technical called keystone correction, and it can be done easily with Photoshop or any other editing program. Many pano stitchers (including AutoPano) have built-in functionality for straightening verticals.

There are so many good tutorials on this technique online that there's no need for us to revisit the topic. Rather, we will just point you to some of the articles that we've found helpful:

• Keystone Correction in Photoshop
• ShiftN Automatic Vertical Straightening Software (Windows only)

A few additional notes are important when considering this technique:

• Keystone corrections means you'll have to crop some of the picture out, so be sure to consider this when shooting. Leave yourself some extra space for cropping or consider shooting a 2-shot pano and cropping it to photo size in post-production.
• It takes time to do the post-production. Consider offering this service as an up-sell on higher-end listings for one or more shots. In many cases just the correcting the front shot will provide a great deal of value for the customer.