Those are definitely termite tubes. Those are the exploratory tubes that termites make when they come out of the soil and are exposed to air and light. They build the tubes out of dirt and their feces to protect them when out of the ground. Definitely termite tunnels. These are common on the side of a house, or inside a crawl space going up foundation walls.
DIY is definitely an option - a MUCH cheaper option. It's really simply in terms of knowing what to do, the hard part is the digging and drilling, but it's worth it when you know how much you will save. Read this article on my site to learn how to do it yourself: http://www.domyownpestcontrol.com/how-to-perform-termite-treatment-a-87.html
I think I have mentioned it on the site before but I used to specialize in buying termite houses. In Arizona they are quite common, in the Midwest not so much.
I disagree with Keshlam in saying it is too much trouble, and walk away. I think the sensible thing to do is figure out what you want out of the house and what it will cost to fix it.
If you want to buy a house an just move in and live there and touch it very little then you shouldn't buy a house with termite damage. In actuality your house choices are going to be extremely limited.
If you would like to update a house and make small living changes, this could be the perfect house for you. In the flipping business we know it is much more cost effective to gut something then work around everything.
How do you assess termite damage. You do it yourself. That is fine that you had someone help. I would go around the house with a fine tooth comb and document any kind of wood damage, any kind of paint damage, any sagging or structural issues. Everything should be attributed to termites.
So the main assessment is centered around if the termite damage is on the outside of the house - most houses are like this or is it pervasive through the whole house. You really need to spend a good deal of time in the attic (trusses, floor beams, and plywood sheathing under roofing) and in the basement looking at the structure. Framing and cosmetic things on the outside of the house can be fixed easily.
The next step is to get a quote from someone that can come in and fix everything on the outside, drywall and simple framing. Double that quote and take that off the price of the house. Remember that home owner has to now disclose this damage to all new people who look at the house. Mention this to them and use it as a negotiation technique.
Really if you aren't looking to make money off the house you need to figure out if you want to manage the fixing of all this stuff to make it look exactly how you want or do you want something that is more move in ready. There is NOTHING wrong with buying a house with heavy termite damage, you just need to set your expectation and it would probably be cheaper and faster if you didn't live in the house while the inside stuff was getting done.
Note: I mention to double your quote because I have found from experience that most termite quotes end up on average at 1.5 times original quote. Double it because you are managing it and might not be living in house for 1-3 months depending on damage. Also I should point out, be fully aware of any asbestos potential (think flooring, popcorn ceiling and ductwork). This is an important caveat because when you start opening stuff to fix termite damage this is really the only thing that can prove to be costly real quick.
Best Answer
Other than learning how to look for exterior telltale signs of termite damage, such as spent casings and holes in the wood or in the ground, you need to write in a contingency on your offer to purchase for a complete home inspection and/or an additional pest inspection.
As mentioned above in the comments, hire your own home inspector and/or pest control specialist. DO NOT succumb to the pressure of Realtors to use their favorite inspectors. Find inspectors that truly work for the person that hires them, you! If you are not trained in building construction, inspection, or pest control, do not attempt to evaluate the condition of a home on your own.
Some Home Inspectors, such as myself, offer screening inspections. This is a simple walk through (apx 1 hour) and initial evaluation of a house before one even makes an offer. This type of inspection is not as comprehensive as a full inspection that can take 2 to 4 hours in home and documents all the aspects of the house, rather it is an hour spent looking for obvious major flaws or situations that will help you determine if you actually want to consider placing an offer. Once you have found a house you are serious about, this screening inspection is usually much cheaper than a full inspection, but since the inspector should be acting as your advocate, can advise you if there are any major issues that would influence your decision to make an offer or not. For the hundred bucks or so, it can be a huge time saver, allow you to make a more realistic offer, and give you a better feeling of confidence about the home you are making an offer on. Good Luck.