The following suggestions were offered by Stu Friedberg --
Get the catalogs and know what you want. There are often many sizes, models, and sources of an "X", so you need to know which particular X when you write and especially when you call to place an order. Even the smallest industrial supply houses deal in tens of thousands of items, which means even very knowledgeable order-takers can't always give you the information you need over the phone. Reserve queries about details for stuff that you couldn't figure out for yourself.
Many of the order takers are very helpful and knowledgeable. At *SOME* sources the order takers can actually go look in the stock bins, take a micrometer to measure a shaft diameter, etc. I have had people at three different companies do something like this for me. However, some companies have computerized centralized order taking at a location completely separate from their stocking locations, so don't *assume* people can tell you anything that's not written in the catalog. I've had one company tell me to just order a set of change gears and return them if I couldn't use them. This wasn't crazy, the order taker simply had no relevant information available.
Get the catalogs and shop around. Very often there are *big* differences in price between identical items, and even more often one source will have a unique or slightly different item at an excellent price compared to the "standard" item. There are lots of reasons for this. I have seen 2 to 1 price ratios on things like shim stock (from the same manufacturer) and "can't twist" clamps (from different manufactures but of equal quality). Occasionally, you will find 10 to 1 price ratios on things like boxes of hose clamps. Great deals if you look around. If you can, examine a tool at a local store (where the prices may be higher) to see what the quality is like, before placing the order by mail or telephone.
You can also learn a great deal by perusing the catalogs, both about tools in general, and about specific details of specific tools. There's seldom enough room in a catalog to print all the manufacturer's data, but different sources will select different stuff to print. I have many times used one company's catalog to select the precise thing I wanted, then bought it from another company because the price was better.
Most suppliers ship quickly if they have a credit card authorization. If they don't ship within two working days on a routine basis, shop somewhere else in the future. One full working day is quite common.
I have had only one bad incident in the 4 or 5 years I've been buying industrial stuff by telephone, and came through with no losses. A supply company (which entered bankruptcy proceedings just a little while ago, by the way) charged my credit card for the full amount of my order, didn't ship for a month, and was completely clueless as to when they would ship my order. That is intolerable, and protection against abuse like that is one good reason to use a credit card rather than sending a check. You don't need to sue to get your money back if the merchant doesn't come through. (If it's not obvious, I got my money back and started to throw out that company's catalogs as they arrived.)
Some industrial suppliers don't do back orders because it slows things down. The stock pickers send what's in stock and mark out of stock items on the invoice. This may be a little different from retail mail order sources you've dealt with in the past. Contact them about what's in stock and when it's expected to be available.
Be prepared to return an item. Having to return an item because it was misshipped, defective, or of unsatisfactory quality is *NOT* an indictment of the supplier. If you do enough shopping for industrial supplies, you will find that you have to do a partial return maybe 1 time in 5. Don't get mad; don't get upset. It's routine. Industrial supply and consumer retail have different expectations about quality control.
When you return an item, follow instructions. Many, but not all, suppliers require you to contact them for a "return authorization" number, which you must write on the outside of the package. You should include a copy of the invoice in the package. This is *NOT* an opportunity for the supplier to screw you over. This is a routine matter, and most of them just ask you to note on the invoice what was wrong and if you want credit, a refund, an exchange for something else, or whatever.