Problems:
1) Most ISP's block necessary ports for hosting a website.
2) Chances are he does not have a fail over generator installed on site. Power flicker or power outage, website is down.
3) Internet goes offline, website is down.
4) Hardware failure of any kind, website is down.
5) Overage on the allowed bandwidth of your internet package, website is down.
See where I am going here? Point of the matter is if you are OK with risking potential customers in an effort to save $10 a month, you may want to re-think your strategy.
1. It is impossible for your ISP to block port 80.. that is every browser out there.. would mean, you get no internet at all.
(speaking on behalf of over 100 dedicated hosting accounts i have created over the united states, dealing with multiple ISPs)
2. A fail over generator.... hmm.. I didnt hear him say he didnt have one, nor that he did. however, Having said that. based upon your power company, demographics, natural disaster area, etc.. power outages are rare and infrequent. The mathematical probability that the power will go out, through power failure, just at the time a potential customer is hoping on the site, is unlikely.
3. Internet goes offline.. True.. but can be fixed with Dynamic DNS (which is free) and a free host like.. 000webhost or something, that runs a dynamic backup. Dynamic DNS cant ping the server, sends it to the next. simple and easy. But my internet has not gone done for 7 months.. and when it did, it was 40 minutes.
4. Hardware of any kind... errr. this is true for shared hosting. Find me a Hosting plan, dedicated or shared.. that this doesnt happen.. and I can show you a liar. hardware dies. Its the nature of our business. It puts food on our plates.
5. Overage on allowed bandwitdh for internet plan.. hmm. unless he is streaming Video and competing with youtube, we can ignore this. Plus, if he is in United States, we dont have such limits (the few cities and companies that do that.. well.. theres always 10 other companies that do not)
Remeber - the idea was the cheapest way to get a website up.
Shared Hosting = There rules, there server, what they support, what they do not, the languages you can use, the file permissions you can set, and the other 100 shared hosting accounts on the same box, fighting for the CPU / ram / Bandwitdh
your box = whatever you want, whenever you want, however you want. All the power of your Celeron 800MHZ 256MB of ram 20 year old PC - at your will.. Is much faster then any Shared hosting plan.
I speak from 14 years of experience in this field. Hundreds of Business clients respect it. They love it. I love it as a developer. I have never had an issue.