I am planning to rent out the condo in AirBnB for medium- to long-term stay in Bangkok Sukhumvit area. However will be needing a company or agency to help with keys and immigration report filling, as well as damage checking and cleaning. Any recommendations?

I'm using air bnb with great success in the same area but I don't get your logic. Since your not living in the area Why not just rent it out with an agent in the first place

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The concept behind AirBnB is that the owner manages it and that is how the owner makes a profit

If you have to pay a management company to do what you describe above then you will have to raise your rate to cover it and then customers are just going to go to a hotel instead of "short time" renting your place

Suggest you sit down with your pencil and figure out if you are still going to be competitive with management expenses, electricity, etc.