Not every refusal is the same refusal
People use "visa denied" for three different events, and the route out of each is different. Getting the category right is the whole of the early work, because two of the three run on a forty-eight hour deadline and the third does not have a statutory appeal at all.
The first is being refused entry at the border as a person the Immigration Act excludes. The second is having permission to stay revoked once you are already in the country. The third is an application refused by a Thai embassy or consulate abroad, before you travel.
The Immigration Act provides a specific appeal for the first two. It says nothing about the third, which is why an honest answer about a consular refusal usually involves reapplying properly rather than appealing.
What a lawyer does with a refusal
The first job is reading the refusal itself. The Immigration Act lists the categories of person excluded from entry, and they range from documentary problems, such as travelling without a valid passport or without a visa where one is required, to substantive ones such as having no appropriate means of living or a previous imprisonment by judgment of a Thai court. Which ground was used decides whether an appeal exists and what it would have to answer.
The second job is the filing itself, inside the deadline and in the prescribed form. This is mechanical work, but it is work that cannot be done late.
The third is the longer game. Where no appeal route exists, or where an appeal has run its course, the useful question becomes what a future application needs to look like and what the record now says. That is a different piece of advice from an appeal, and a firm should be clear with you about which one you are buying.
Routine applications and extensions, by contrast, are handled by visa agencies in Thailand rather than by lawyers. Extensions of stay and changes of visa type are dealt with at the immigration office for the province where you live.
When it is worth engaging someone
If you have been handed a written order, immediately, because the deadline is measured in hours rather than days. If your application was refused at an embassy abroad and you have time before you need to travel, the value is in getting the next application right rather than in an appeal that the Act does not provide.
Be wary of anyone who promises a reversal. Both statutory appeals end in a decision the Act itself describes as final, and no firm controls that outcome. What a firm can control is whether the appeal was filed in time, in the right form, and answering the right ground.
On fees, an appeal against a refusal is a bounded piece of work with a defined scope, and most firms quote it as a fixed fee. A matter that runs into detention or a formal proceeding cannot be scoped the same way and is usually billed hourly. No credible published source gives professional fee ranges for this work, so ask for a written quote and check what it covers.
Where a refusal has already turned into a removal, overstay and deportation covers what happens next, and contested matters that go further are dealt with under immigration proceedings. An immigration lawyer in Thailand handles all of these together.
This page is general information, not legal advice. Rules and procedures change, and whether a route exists depends on the exact ground used, so speak with a qualified professional about your own refusal.