There is a script on there that can be uploaded to create a custom .exe of UltraVNC, allowing them to connect directly to you. On the link above, there is a sample configuration file that looks quite a bit more complicated than it needs to be. Here is a very simple setup:
[TITLE] Savvy PC Repair [HOST] Savvy PC Repair (Double-Click) -connect 192.168.1.101:5500 -noregistry [TEXTTOP] [TEXTRTOP] [TEXTCLOSEBUTTON] Disconnect [TEXTMIDDLE] [TEXTBOTTOM] [TEXTRMIDDLE] [TEXTRBOTTOM] [WEBPAGE]
You can add more details as per their example, but what I listed is enough to get them connected to you. Replace the IP with your IP address. Be sure you have port 5500 forwarded in your router. Name the above code something such as helpdesk.txt (like their example). Not sure if you have to follow their naming schemes, but probably not. Create a .zip file called custom.zip (again, your own names will most likely work, could be completely wrong though). Go to the Upload Site to create the custom UltraVNC .exe file and save it somewhere handy. Email it to the customer, or upload somewhere and give them the link. The idea is to run UltraVNC in Listen Mode on the machine you wish to view from, and have the target run the file you just created. Surely is not a beautiful helper application, but it works:
On the viewer PC you should see the following:
Now you have a VNC connection to their PC, without having to worry about them changing firewall settings, doing port forwarding, or even installing a program:
Again, if you are not using TeamViewer over their allowed limit, you can simply stick with it (or other free solutions you may find). This just seems to be a good alternative to paying for other remote support software. I hope somebody found this guide useful.