It's All Subjective:
I can say a rendering is bad and the average person off the street might say they see nothing wrong with it, so why should anyone care? This is the dilemma many potential clients face, bottom line is the all mighty dollar and if a cheap $500.00 rendering conveys the idea to the average person, why not just go with the cheapest artist/studio you can find? If it serves your purpose, it is hard to argue against it, and probably a waste of time to even try. So rather than argue the subjective, lets discuss the objective.

$500.00 vs. $1,500.00 Rendering:
The little guy in a foreign country using pirated software and hardware supplemented by their government doesn't have the overhead of a big professional studio. Obviously you can reverse the scenario and the little guy in our country using pirated software working from home has less overhead than a big studio in a foreign country, this isn't about foreign vs. domestic, just pointing out the more typical scenario based from my experience. So pricing doesn't necessarily denote quality so that $500.00 rendering is looking pretty good right about now.

 In any case the little guy typically can whip out a rendering that is probably acceptable and you are dealing with an individual which a lot of people like.  That $500.00 rendering can also come from a large studio that is basically a render mill pumping out renderings at a very fast pace by the use of hundreds of artist working for cheap, producing renderings via assembly line fashion.  Down side is usually that you get different people of varying skill levels each time that studio provides services. What it can come down to is the big studio has back up artist to complete your project if initial artist gets sick or has an emergency comes up, but you aren't guaranteed the same artist working for you from project to project. So at this point there really isn't much mentioned here that helps a potential client make better decision.

For an American company seeking artist specializing in AEC, choosing an American artist/studio who has a strong foundation in our construction industry is a huge bonus in the long run. If you go with someone who doesn't have a strong architectural background you will probably need to assign someone in your office to coordinate with them and this cost you money and adds up real fast. There is also the whole English as a second language which can sometimes make communication less than accurate. Now that $500.00 rendering starts costing a lot more.  

Having someone who knows National materials, construction techniques and codes is very beneficial saves lots of time for the Client who doesn't have to hold their hand every step of the way. Little things like handrail balusters spaces less than 4" apart or 6" high curbs can make a rendering appear correctly and not steal the viewers attention trying to figure out what doesn't look quite right. So a trained professional who charges more can actually save money for the client and more importantly can save a lot of heart ache and revisions.

Selecting an artist/studio by their online portfolio can be difficult for multiple reasons, so if in doubt ask for a reference. There have been plenty of situations where online artist/studios have been called out on stealing others work and showing it as their own. Another item that isn't illegal but questionable is that there are companies out there that sell readymade scenes for people to render and put in their portfolios. The scenes are sold for this purpose, so nothing illegal, but artist/studios are using content no created in-house to pad/build their portfolio, the work doesn't represent what they can do and is misleading. There are also plenty of cases where and artist was a small part of a team and they go off on their own and show the work as their own. So be careful if the work seems world class, but the price is ridiculously low and they can't provide a referral or two.

What it comes down to is finding the artist/studio that is knowledgeable in your industry sector and who has a body of work that you respect and a point of contact that you feel comfortable with at a price point that is in your realistic budget. No simple answers just some things to think about, we have found that there are some fantastic artist/studios in China and the old Soviet Union countries like Serbia or the Ukraine, so it doesn't mean you can't go outside the country to find great reliable talent, just do a bit of homework and make sure you aren't going to do a lot of hand holding or an end product that isn't acceptable. Good luck and if we can provide you with a proposal or help out in any way we would be glad to be of assistance.