I'm looking for advice on how to correctly communicate pixel art requirements.

I keep getting disappointing results despite my best attempts to keep requirements clear. This is not just wasting money, but it's a great time-stealer as well.

I'm posting here hoping that someone could offer some suggestions.

This is what I have been asking for, and been using as a base specification (together with a list of tiles)

- Colours and atmosphere in the spirit of the lush grass and forests of these examples: http://imgur.com/a/CT3kJ
- Map tiles are standard old school orthogonal 2D: http://imgur.com/a/E6npN
- Buildings to be rendered at an unusually low angle, like this: http://lazarus.elte.hu/hun/digkonyv/szakdolg/katona/image/amiga_game/010_01_defender_of_the_crown.jpg
- Examples of really awesome buildings: http://jonik9i.deviantart.com/art/Buildings-for-game-4-190858434

Then I go on and explain:

- Tiles are either 32x32 or 48x48 at the smallest size, and a hires version with no additional details at twice that resolution.
- We can use various software rendering techniques to make things like grassland look less repetitious.

Problems so far:

- The palette, people really have difficulty understanding what the difference if between the examples I give and the usual palettes (like this one http://static.tvtropes.org/pmwiki/pub/images/wesnoth-1_9_0-3_1640.jpg)
- People don't understand the limitations when constructing 32x32 buildings, so we get things with impossibly many details, that don't look good on a small screen. Like they try to draw a city using 3-4 different towers in a 32x32 square. I would expect them going for a simple design with perhaps a tower and a city wall.
- Some don't understand that a large palette is allowed and create something things that look like buildings from an 8-bit game.
- Because most good pixel art is isometric, I'm often forced to use those as reference for colours and textures. I keep saying that these only show the colour and texture, but that doesn't stop people from repeatedly asking if I want isometric art instead.

I'm trying to give images as examples and I am surprised how little effect my examples have on the direction of the art.

I keep wondering why I keep getting results that differ greatly (in both style and colour) from the examples I give and I'm grateful for any advice I can get in order to be able to properly communicate the art direction for the map.

Help?