As far as I know, Grainger will sell to anyone, but will only give good prices to large companies who know how to give the salesman the best hand jobs.
I can't stand dealing with companies who play favorites with accounts. Offer your products at a fair price with no gimmicks and good service and I will buy from you. Make me deal with a ****** salesman who is pushy and makes me jump through hoops to get the same price as McMaster, well, go **** yourself. I will buy elsewhere.
A few years ago I was given the task of setting up a company toolbox for the maintenance department. I made a list, brand names and part numbers. Put it out for bid. Grainger won the bid with the lowest price. When the order came in, I discovered the salesman had replaced stuff with their ****** Westward house brand to cut costs and win the bid. That was the last time I ever had Grainger quote anything.
Grainger gives vacations and other incentives to purchasing agents who buy from them over other vendors. A company I worked at found out the purchasing agent was getting vacations from Grainger and spending WAY more money with them vs other vendors. She didn't last long with us.
For the life of me, I don't know why people buy things from them. I can get literally anything they sell from another vendor cheaper and with less hassle.
OP, if you take the quote for a Miller table to another company, they are very likely to match the Grainger price. I know my welding supply house has told me point blank they will match or beat Grainger's price even if they lose money on a few things because its worth it to them to take Grainger's business.