The numbers. The statistics. Some folks just want to see the data and the way the numbers pan out. They may or may not take your word for it, but some just want to see the proof, the evidence, the data results for themselves to then draw their own conclusions.
As for gender selection, this may be off-putting to many who do not know he data surrounding the topic. PGD or preimplantation genetic diagnosis, has a very high success rate. See what this means at http://www.gender-baby.com/about-us/success-rates. If more services are needed, that can be arranged as well. Donor eggs, donor sperm, frozen eggs, frozen embryos, all of those are plausible options depending on your current situation as well. It is not a one size fits all kind of deal. Each family has unique needs and those can generally be met within reason. The good news is that the success rates are high for these kinds of procedures. The biggest factor is mainly age in the mother who will be carrying the child(ren). Other than that in the realm of gender selection the odds are actually in your favor!