Should I choose an SEO company that does everything in-house?
Not as a rule: a company that does everything with its own staff offers one standard and one team to answer for the work; a company that brings in specialists for some tasks can offer expertise a small in-house team cannot keep on salary. Either can do good or poor work. What decides the matter is whether the company tells you who does each part of the work, how it reviews work done by others, and who is accountable to you for all of it.
What each model offers
A fully in-house team follows one process, shares what it learns across accounts, and leaves no gap between the people who plan the work and the people who do it. When something goes wrong, there is one team to fix it. The limit is range: a small company may not have a full-time specialist in every area your site needs, such as technical work on a complex platform, digital PR, or content in a regulated field.
A company that uses specialists can match each task to someone who does that work every day and scale up or down with the project. One sound arrangement keeps strategy and account management in-house while specific execution, such as technical fixes or content production, goes to vetted specialists. The risk is uneven quality where a specialist is poorly briefed or loosely reviewed.
Ask for a staffing map
Instead of asking whether the company uses contractors, ask for a map of your account: each type of work, who does it, whether that person is staff or a contractor, and who reviews it before it reaches you. A company that can produce this has thought about it; one that cannot may not know itself. The map also tells you who to ask when something in a report needs explaining.
Access and accountability
Every person who works on your site, staff or contractor, should have their own access to the accounts they need, with only the permissions their task requires, never a shared password. That keeps a record of who changed what and lets you remove one person’s access without disrupting the rest. Whatever the model, the agreement should name one company as responsible for all the work, including any part done by others, and should settle who owns what the specialists produce.
Choosing between them
If you value a single team and a single standard above access to specialists, prefer a fully in-house company. If your site needs depth in an area a small team cannot staff, a company that uses specialists may serve you better. In both cases, judge the company by its work for sites like yours, its staffing map, and how it reviews the work, not by the label it gives its staffing.