I have been on both sides of this fence. I managed a couple of different supply houses when I was younger and for the last 18+years have moved to the contractor side, doing the buying.
On the supply house side, I never liked doing business with people that just cherry picked a few of the low margin items. I always tried to give a fair overall quote and hopefully with the service that was provided, both before and after the sale, there would be a value to the contractor to award the job to me.
I also disliked being offered another look, as this usually meant that, that contractor was just taking the second look to another supply house and offering them another look etc. It is a zero sum game, way too much work for very little profit at the end of it.
Occasionally on a simple drop ship order I might have entertained it.
Now, as purchaser, I fax / email out quotes I expect to get the best price the first time from a supply house.
I will not offer another look to suppliers, if and when they find out, your doing that, they rarely will be straight up in the future.
I award the sale to the low price supplier, assuming everything is available when its needed. If not I will go to the next lowest.
I almost always group similar items when requesting quotes. I will send out a separate quote for wire, boxes, pipe, special gear, fixtures, and then miscellaneous materials.
We of course have rebates set up for normal service gear, circuit breakers, and devices, so the supply houses with those items don't need to quote, the prices are fixed by the manufacturers.
If I do not get the service I expect from the supply house I simply don't buy from them, and there have been a few through the years that had zero dollars in sales to us.
If I don't have time, or don't want to do research into a particular item, and I ask a supplier to do it, they will always get the order. I wouldn't think of shopping it around after they have invested their time and resources into getting me the answers I need.
Side note:
The grass is much greener on the contractor side of the fence! You have 5+ supply houses, the internet, and the big box stores to find what you need, when you need it, at the price you want to pay. Our company only uses the internet and the box stores as a last resort, the supply houses need to stay in business for the oddball stuff required for our operation. We will gladly pay a little more and do the business locally. It also has the very real side benefit of easy returns on defective items, and keeping the local economy going.
On the supply house side you are stuck between a manufacturer lying about a deliver date and an irate customer that needed it yesterday.:rant: