Back in the day when I was fairly new to monetization, I had some domains at service X, some at service Y, and some at Domainspa. Results at Domainspa looked great. A few days before the end of the first pay period I received a somewhat cryptic msg asking me to "explain the source of traffic" for a few of my domains. I sent back a msg explaining that they were porn sites in the past and had traffic.
The day before the end of the pay period, I tried logging into my account and got a message that my account had been suspended.
I moved those domains to another service (one of the X and Y I mentioned above) and am earning money from them.
The experience left a bad taste in my mouth.
Also, if you look around this forum or the monetization section of other sites that have forums about domains (e.g. DNF) you will find one of two things - very little mention of domainspa in comparison to other parking services, and/or reports similar to mine - accounts being shut down right before the first payout date.
Ooh forgot, should have mentioned two things:
1. I sent Acroplix a PM before sending this, got his reply, I offered to provide info that could be substantiated and got a nice reply but no interest in substantitaing my info. thanks a lot! Interesting stuff.
2. the reputable providers that I have seen a lot of good info posted about are:
sedo.com
parked.com
namedrive.com
godaddy.com/cashparking
domainsponsor.com
fabulous.com
I would park domains at any of these and see how the results go before going with domainspa. I may be forgetting one or two, but these are ones I know firsthand to be reputable.