Quick answer
Do love spells actually work?
Every spell belongs to a system: a set of rules someone defined or inherited, with its own conditions and its own price. A love spell is no different. When you are aligned with the system it comes from, it can work. When you are not, nothing happens.
The trouble starts with where most people get them. A spell bought from a half-baked witch on Etsy usually lands in one of two places. Either it does nothing and you have lost some money, or it works and quietly ties you to a pact you would never have agreed to if you had known what it carried.
If you want someone, look first at what actually stands between you and them. A consultation can look at that directly without locking you into anyone's system. The longer case against shop-bought magic is in why you should never cast a spell you found on the internet.
Questions
Why do some love spells do nothing?
Because you are not aligned with the system the spell comes from, or because the seller never had a working spell to begin with.
What is the risk of a love spell that does work?
A spell that works ties you to the system behind it. Bought from a stranger, that can mean a pact whose terms you never saw.