For designers and developers, this is the most natural use of the programme.
THE SITUATION
You build a site for a client and they need hosting. You recommend us. They order through your link and you earn commission.
This is entirely legitimate, provided the client places and holds the order themselves.
DO IT PROPERLY
Recommend hosting that actually suits the client, not whichever pays most. Your relationship with them is worth more than any commission. Tell them you earn a commission. Most clients do not mind, and discovering it later looks bad. Let them hold their own account, which is cleaner for both of you when the relationship ends.
WHAT IS NOT ALLOWED
Ordering under your own account and claiming the commission. That is self-referral.
THE ALTERNATIVE WORTH CONSIDERING
If you host many clients, reseller hosting may serve you better than affiliate commission. You control pricing, branding and the relationship, and the margin is usually higher than commission.
Affiliate suits occasional referrals. Reseller suits a hosting business.