“A chain is only as strong as its weakest link.” (paraphrased Thomas Reid)

If your site is on a shared hosting server, it is only as secure as the site with the weakest security on the same server. Similarly your site must compete for resources with the rest of the sites being hosting on that server instance.

1. If any one site on the server is compromised, it literally opens a gateway for the attacker to gain access to the other sites hosted on the same server as well.
2. A malicious user can buy the hosting from a shared hosting Provider and use his site to gain access to other sites on the same server.
3. There is also the disadvantage of not being able to harden the server. If you are on a shared hosting server, you would not have access to the PHP and Apache configuration of the server.
4. Clients of shared hosting solutions often share an IP address with other clients. If your neighboring client on the server ends up an a spam blacklist, everyone else using that IP will also be on the same blacklist. If another client on the same server instance is the target of a Denial of Service attack, you will too.
5. With shared web hosting, you will be sharing CPU and memory with your neighbors. As CPU and RAM share resources, you will be provided with a guaranteed amount of disk space. It is possible that one of your neighbors utilizes more than his/her fair share and it can adversely affect you and other users.

Risks of 3rd-party payment settlement services.

1. Your customer data is not your own. A shared payment settlement service has access to and can potentially sell the names, demographics, and other metadata around your customers transactions without your knowledge.
2. You may pay higher fees than necessary for the “benefit” of a shared service.  Typical shared service providers such as Paypal or others will charge a 3% + 30 cent transaction fee for each payment that goes through its gateway, while paying a lesser fee to the actual credit card merchant provider.
3. Shared provider insolvency is a big risk. The shared provider is actually collecting the money from the bank for a payment then transferring that money to you. If at any time those accounts are insolvent for any reason, you may find the money you expect to receive has disappeared.