The appearance of a website doesn't necessarily mean the service is good or bad, but in my experience and reading the experiences of some users in this forum, even the best designed websites can be run by unscrupulous people.
When considering using a writing service, I'd pay close attention to:
1. The knowledge and friendliness of the support staff when you are making contact.
2. Is the support staff easy to contact (during business hours, which should be posted somewhere on the respective website)?
3. Is the website free of grammar errors? (This is not to say that you won't find a single error anywhere on the website as designers are human and prone to err, but generally you can spot the difference if you take the time to review more than the main pages.)
4. If you placed and paid for your order, how is the responsiveness of the support staff and your writer, if you can contact the writer directly. If not, how is the writer's responsiveness through the company's system? (A good company is one that is attentive before, during, and even after the sale is complete. That is how a new client becomes a repeat client. Some companies stay in close contact while trying to obtain your business but once you make the payment, their attentiveness dwindles. Of course, during peak times, it may take longer to respond to clients, but generally a company's support staff should reply to clients within a few hours or at least the same day (when really swamped).)
5. What is the company's policy on difficult orders? I don't accept a project that I am not 100% confident I can complete, but many companies (and some indie writers will). If your project is more complex than originally thought, will the company let you know quickly and refund your money?
There are many other things to watch for and questions to ask, but this is a start.
Overall, the way a website looks is simply not enough to let you know how the company and its writers will treat you nor does it prove the quality of the work you will receive.
In fact, I have a former colleague who now operates her own writing company. Her website is simple. It's attractive enough but not "beautiful." It doesn't offer the option to pay for the order when submitting it. Clients must wait on the company to email the price and then they pay via the accepted methods. It works for her and she can better vet the projects that she may not have a qualified writer for. Now, that is not to say that companies that do have "pay now" options don't vet. I just used my friend as an example to illustrate that beauty does not equal quality and vice versa.