Hey @Juyoung Cho. Im an investor and mortgagre broker in Halifax, NS. I always estimate my ARV with market comps and if its multifamily (5+ unit) I use a mix of comps + income approach.
I read through some comments and sounds like some US investors do things a bit differently there. For my investments (in halifax), if i find a property that looks like there is potential based on my numbers, I will get it under contract, then have as "AS-IS" and "AS-COMPLETE" appraisal done. The as-is will be needed for the bank, and the as-complete will give you a more confident ARV to base your refi off of. We typically dont move forward with the project if the as-complete appraisal does not come in where we need it to be.
Note: Not many brokerages work this way. I work with an investor focused brokerage that specializes in these types of project.
Last note, I've found the income approach is quite strict in the US, however at least in halifax, appraisers use a balance of income, comparable and cost approach. Our financing in Canada is much much more strict than US...
Hope this help. If you have more questions feel free to DM me