I work with numerous agencies as a creative writer (WPs, press releases, stuff like that), and the trend I'm seeing is that they are now rebranding themselves from ICO promotion agencies into IEO agencies. So very soon you'll see dozens of them promising to get you listed on the largest IEO exchanges, "package" your project and team, and so forth. Substantially, nothing changes - it's still the same people doing the same thing - but under a different name and for a higher price tag, since IEOs are supposed to be more costly.
Half of these agencies are based in Russia. This doesn't mean that they offer a poor service - I know dozens of talented people who work for them. But their business model is typically Russian: earn as much as you can, as quickly as you can, and with as little effort as you can. What you should understand is that IEO agencies employ freelancers (writers, designers, marketers, SMM people, etc.) and slap a huge commission on top of these freelancers' rates. So for example, I charge about $1000 for a White Paper, and the designer I work with charges a further $200, but the agency's client will pay upwards of $3000 for the WP package. So if you are planning an IEO, I see no reason why you shouldn't assemble your own freelancer team - it will save you tons of money!
Would agree with this post. Finding freelancers on bitcointalk, or fiver even is way cheaper than hiring a special marketing/consultation/advisory firm.
There are cons and pros to this though, 100 percent. Freelancers are much unreliable than an actual company, and in many cases, aren't as high quality then hiring a full firm. Firms are much more stable, less to cause issues and reputable then single individuals. If you can get a decent price on a full package from a marketing firm, I'd recommend you to go with that.