What is the difference between condominiums and apartments?

The main difference between a condominium and an apartment is with regards to ownership. An apartment is owned by an individual or company who rents the units out on a short or long term basis. A condominium on the other hand is owned by individuals who are the shareholders of the property. Each individual shareholder contributes a monthly maintenance fee.
In terms of facilities, apartments and condominiums are comparable to each other.
Condominiums are more likely to have outdoor facilities like children's playground and garden.

What is the difference between serviced apartments and apartments?

Serviced apartments are in general luxurious buildings offering a wide range of facilities. They cater mainly for expatriates and business people. Short term rentals are also available. Whether on a daily or weekly basis, serviced apartments can offer this flexibility.
Apartments are mainly for long term lease with a minimum period of one year. The facilities vary from apartments to apartments.

Does hiring a real estate agent involve a fee or commission?

In Bangkok, hiring a real estate agent for residential leasing does not involve any fee
or commission if you are the aspiring tenant. The commission is paid by the landlords.

What are the minimum rental contract and the standard terms and conditions?

The minimum rental period is usually one year for most apartments and condominiums. A two month deposit and one month advance rent is required. The deposit will be refunded one month after the rental lease is up. There may be deductions for unpaid utilities and phone bills.

What if I need to leave the country before the lease is up?

The deposit will be forfeited if the rental lease is not up yet.
A diplomatic clause can be put in place to prevent this from happening.
This clause is required by multinationals as they are likely to transfer employees from place to place.
However, in Bangkok, landlords will normally require a minimum period of stay of 6 to 12 months before the clause can be effective. After fulfilling the minimum stay period, a 60 day prior notification and company supporting documents need to be provided and the deposit will be returned.