Something I have seen kind of stated, but I know for a fact is a reason, considering I am a professional auto tech.
If you just walk on to a businesses property, say a repair shop, while the SO guy is there and just strike up a conversation and start buying tools from him, did you ever think you are stepping on that shop's toes? Firstly, the techs usually don't get enough time to do all the business and get all the transactions they need done as is. They poor tool guy is being pulled in different directions by each tech and still has a schedule to make. Maybe an individual tech doesn't spend as much money as someone in a more lucrative career, but when a shop has 15 techs, then I can promise you, you aren't ever spending close to what he makes off one visit to that shop each week.
If you are at a place of business unannounced and uninvited, you are probably ******* off the techs and managers. Firstly, what are you doing here? We have a job to do and a living to make, do you give that shop any business? Or are you just trying to buy tools so you can remove the shop from the equation and fix your car yourself? If you don't give that shop any business, chances are the techs or managers there are asking the SO guy to not keep indulging you or to not indulge you at all.
If you truly want to get in with the SO guy, talk to one of the shops, get in good with them and see if they will introduce you. Otherwise catch the SO guy at lunch or the bank, he may have a very different attitude when not in front of a much more lucrative account that is not very happy to see you on their property for no good reason.
Also, my SO guy is pretty peeved with Joe Random, because more often than not, they walk on the truck and get a healthy dose of sticker shock. I doubt most people are use to buying 1 wrench at the same price as an entire set of the economy store brand. They usually go in with a talk of a big spending game and then realize 100.00 isn't getting you much. They then leave and never show up again. In all fairness to the SO guys, that truly is a waste of time for them and I am sure that is the more likely scenario. I hate having to need SO quality tools, as much as I love them, because even after years in the industry, the prices are hard to swallow. A Solus cost more today than the top of the line computer would cost in 98. I can buy a laptop and cables and software to do all the same things for under 1500.00.