Doesn't matter if someone is spending £5 or £100+ if I say I offer something I offer it, if I don't I will say so and won't. Wearing a special outfit, or combination of clothing for a regular really makes them happy, so long as I have it and have notice it's no problem. If someone asks me at short notice then if there's enough notice then I will. I don't keep a range of uniforms or outfits because it's not me, and because they just wouldn't get requested, most of my clients like lingerie and real clothes - from which quite a few looks including secretary (who has these anyway!) can be quickly organised. I'm also not going to rush out and buy something I wouldn't normally wear, or doesn't suit me on a whim, but if it's for a regular client I've seen quite a few times, well for them I have been known to make the occasional various purchase and it's been most appreciated. I would be reluctant to wear, or not wear certain things for new clients, I'm not going to answer the door naked, or half-dressed for example and the 'bikini, heels and socks' man was probably pushing his luck, but he never showed up.
I would also suppose it might depend on how long the SP is in business for, how many clients she sees. I and ladies like Paris have had plenty of time to build up our wardrobes, someone starting out might not see the point or have had the chance and a lot of the outfits sold in sex shops, Ann Summers etc are really unpleasant and badly fitting. Took me 6 years to find a nurses outfit that I was happy with.